What you refer to is the "W-body", here's a good article:
W-Body History
In 1988, GM revealed the totally new Pontiac Grand Prix, the Buick Regal, and the Oldsmobile Cutlass. They G-Body title was dropped and the W-Body name was picked up as the new chassis label. These cars were changed (from the RWD G-Body) to be a front wheel drive with a responsive V6 and a lot of character to offer. Motor Trend magazine noticed GMs changes as well, giving the Pontiac Grand Prix the 1988 Car of the Year Award for outstanding options and overall styling.
The Grand Prix, Regal and Cutlass were only available with a 2.8 liter V6 engine with either a 4 speed auto or 5 speed manual transmission. The drive-train we very reliable and put out a mere 130 horsepower and 150 ft/lbs of torque.
In 1989, the 2.8 liter had its last year ever and the existing blocks were stroked to 3.1 liters, but this engine was only available with an automatic. The 2.8 liter / 5-speed combo remained as an option. Bowing to outside pressures, Pontiac finally introduced a high-performance version of the new Grand Prix. It was a basic car that was fitted with Pontiacs new 3.1 liter turbocharged V6 and then shipped to McLaren / ASC for final conversion assembly. The package consisted of the turbo V6, a high performance 4 speed auto transmission, upgraded suspension and wheels with 245/50R16 Goodyear Gatorbacks, with extensive aero body cladding. They were available in black or red and they were produced in very limited numbers. In 1990, the Grand Prix STE was available with the 3.1 liter turbocharged V6 but as a four door sedan available in maroon and white. Oldsmobile came out with the International Version of the Cutlass, with a digital dash and many custom options that were never offered before. The Regal backed up the Cutlass along with it's long list of interior packages and options. With the success of the selling numbers in the those two years, GM decided to expand on the W-Body.
1990 marked many new things from GM. First off, 1990 was the first year a four door Grand Prix and it was offered a newly designed 4 cylinder engine; the 2.3 liter Quad-4 High Output. Second, Chevrolet released the Lumina, the four edition to the W-Body line. It was a four door family sedan, rather than a sport coupe Pontiac had to offer. Again, the 3.1 liter V6 was standard and the Lumina had various levels of trim and options. Finally, Buick stepped up and offered comfort and styling for the Regal, which also had the 3.1 liter V6.
For 1991, GM added on the fun to the W-Body line up by producing three high performance coupes: the Lumina Z34, the Grand Prix GTP, and the Regal GS. Unfortunately the Turbo Coupe was dropped from the line up for 1991 and was never seen again. Nonetheless, the GTP offered everything the turbo coupe had, but the car acquired the new 200 horsepower 3.4 liter Twin Dual Cam V6. The twin camer could be installed in the Grand Prix, Lumina Euro and Z34 and the Cutlass SL coupe, but the Z34, SE/GTP and the SL coupes was lucky enough to have a manual 5 speed Getrag transmission if requested. But the Regal got the biggest gain, aquiring the 3.8 liter V6. With the Pontiac Bonnevlle, the Regal claimed the most torque out of the group with 225 ft/lbs backing that up with 170 horsepower. Overall, the vehicles came standard with the GM HydroMatic four speed automatic transmission. As well as performance, all the front fasicas on all the coupes were re-styled to give the vehicles a more sporty appearance.
During 1992, very little changes were made to all vehicles. Only trim and option packages were changed around to benefit the public of consumer wants. Other than that, everything else was unchanged. As well for 1993, no changes were made to the W-Body. Sales were good for General Motors, the Lumina was a very dependable family sedan and a proven winning race car on the NASCAR circuit, the Grand Prix dominated over the Taurus SHO on the streets and the Cutlass was a complete sleeper if in control by the right driver. Overall, the W-Body made a very nice impression on the automotive world.
General Motors toned it down a bit in 1994, by simplifying the model options. Pontiac now only offered up the SE or GT sedan and SE or GTP coupe. The SE sedan had the 3.1 liter V6 and the GT sedan had the 3.4 liter Twin Dual Cam V6. A Special Edition coupe package made the SE coupe just like the GTP coupe. The aero cladding on the GTP and Special Edition SE coupes were cleaned up slightly and the dashboards were redesigned incorporating dual air-bags. The Regal sat on the backburner with nothing major changed, since it's sales were good, and the quality was above all other W-Bodies. This was the last year for the Lumina Euro and Z34 coupe.
In 1995, the 3.4 liter Twin Dual Cam V6 engine was slightly changed to increase performance to 210 horsepower and 215 ft/lbs of torque. The final edition came this year with Chevrolet Monte Carlo, being the two-door counter-part of the Lumina, which was now only a four door sedan. The Monte Carlo assumed the Z34 badge from the Lumina and had the twin camer? drive-train installed.
For the last year (1996) of the W-Body (generation), the Pontiac coupes received the aero cladding as standard equipment, but nothing major was changed overall for all the vehicles. Again option packages and sort were slightly differed, and this was the last year for the 3.4 liter Twin Dual Cam V6. Sales were slightly starting to drop from the line and heading towards the small compact import industry. GM decided it needed to update its look for 1997. The Grand Prix and Regal would acquire a updated Series II 3.8 liter supercharged V6, the Monte Carlo and Lumina would share the 3.1 liter SFI V6 and the Series II 3.8 liter V6, and the Cutlass would be downsized to become a brother of the redesigned Chevrolet Malibu.
Today, the W-Body has grown to the new Chevrolet Impala (replacing the Lumina) and the Oldsmobile Intrigue. All have a considerable amount of prestiege and power. Don't forget where it all came from first back in 1988; hopefully for being the first generation we'll get a little respect later down the road...
http://redfox340.tripod.com/wbodyperformance/id1.html
Pontiac Grand Prix shares its platform with the Buick Century and Regal, Chevrolet Impala and Monte Carlo, and the Oldsmobile Intrigue. Essentially unchanged in year-to-year sales for calendar 2000. Pontiac Grand Prix's next redesign has been rescheduled for model-year 2005, two years later than previously reported. The coupe body style may be dropped, but sedans will share a new "W-body" platform with the next-generation Buick Regal and Chevrolet Impala/Monte Carlo, also due for '05. All are said to be slightly wider outside and roomier inside than today's Pontiac models.
http://www.pontiac-autoparts.com/links1.shtml
GM-W (mid/large): Chevy/Pontiac/Olds/Buick: Impala/MonteCarlo/GrandPrix/Intrigue/Century/Regal (mainly sold in North America, some export of Impala)
Probably will continue for some models with a redesign.
W-body has been modified twice already since intro in 1988.
http://www.globalauto.org/platforms.htm