I've posted this maybe 100 times, but here it is again. There are ways to make the T5 and a 3.07~3.08 rear work together. Here's one:
OEM 3 speed ratios were 2.94, 1.68 and 1.00. With a 4.11 rear, the overall ratios were 12.08, 6.90 and 4.11 (naturally). And this worked very well with the 3 speed up to the point where the 235 got uncomfortable.
With the T5 (correct ratios) and a 3.07 rear, I have 4.03, 2.37, 1.49, 1.00 and .86. And the overall ratios are 12.37, 7.27, 4,57, 3.07 and 2.64. And if you look, you'll see the first three speeds are very close to the original ratios the GM engineers wanted the AD truck to have. And so to drive it you'll feel almost exactly like you're in the same old 3 speed setup...until you get to 4th. At that point your engine rpm will drop by 25%. And then in 5th if you're on a relatively flat highway without too much of a headwind, you'll drive comfortably at around 2000~2100 rpm at 65 mph. When you get into hills or a notable headwind, drop back to 4th. You're still just fine.
