The warranty is only good for 5 years. I would keep this truck for at least double that...
You can get a Silverado/Sierra with the 6.2!!! for 42k. That's the LTZ package. Factor in discounts and that is pretty close to the price of a loaded Colorado, and I just am not a fan of that 3.6 for truck duty...
And then there's the SS with the MANUAL TRANS!! and MAGNETIC RIDE! for just a few dollars more...
See where I am going with this?
Not really.
A. People shouldn't buy mid size trucks to pull 7000lbs..
B. The price you're quoting for 6.2l LTZ Silverados is nowhere near $42K. You can't say negotiated price on Silverados is near sticker price on Canyons because you can negotiate on Canyons as well.
C. As far as I know, there is no diesel Canyon. (so you seem to be saying "They should build me a $25K truck that makes their $35K trucks obsolete.")
On your original topic, I bought a 4.3l Silverado, pretty loaded. I tow around 3000lbs with it pretty easily. It has 90% of the torque and hp my 2010 5.3l Silverado had at the same RPMs, so it seems fairly similar. (and when I have E85 in it, 95% hp, same torque as 2010 5.3l had)
That said, I was troubled to see no external cooler on a full size truck with a tow package rated at 6700lbs SAE towing.
What I see on normal highway/town transmission temps towing is 110-120. The worst I've seen was on a winding, hilly back road where the speed limit switched from 20 to 55 about every half mile, so I was constantly braking and accelerating. Stayed in the 130-140 range there.
I've seen on the web posts from GM staff that said not to worry about temp on new transmission fluid until 140 from one guy, and 170 from another.
There is no OEM cooler for my truck, and the place I bought it recommends I don't put an aftermarket one on.