One comment about newer GMC's (2007 model on up) 6 speed transmission seems to have eliminated the "weak" transmissions in the past 4 speed of GM trucks and SUV. It has a considerably lower 1st gear (4.027and a slightly higher 6th gear (0.667) . (Of course the true 4 X 4 version has a low range which drops the gears by 2.72 more--so you can really grind out of that ramp with a final ratio of about 28:1., with a 3.08 rear ). It also has manual shifting, so you can drop it down for compression breaking on steep grades.