My 2009 Suburban has the 5.3L engine w/ 6 speed auto tranny and 122,000 miles. Fluid reads good level. It starts fine but upon putting it in any gear it will not go forward or back. After restarting it the vehicle may go into drive for 10 seconds and slip forward but then quits going forward again. If I step on pedal in drive/reverse the tach responds but no movement whatsoever. Tried 2 WD & 4 WD with same result. Any ideas would be greatly appreciated!