Please see this post from a week or so ago:
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1498381/1.htmlThere are ways you can make the T5 work in the AD truck and have the first 3 speeds operate almost indistinguishable from the original (stock) AD setup. That is to say you will still be able to use it as a pickup. People occasionally tell me there's no way I could use a 3.07 rear end in a pickup or that I'm mistaken about my rear end gearing, but really it is all a matter of math and understanding the engineers who designed these trucks knew what they were doing. We're working on preparing a report that explains gear ratios, ratio options, etc and our hope is to make it a sticky message that will be easily accessible. With the original AD scheme, you had a rear end with a ratio of 4.11 and a transmission that began with a first gear ratio of 2.94...that gave you an overall first gear ratio of 12.08 (ideal for a half ton pickup with an inline 6). In my case I simply flipped the formula end over end and went with a first gear of 4.03 and a rear end of 3.07...which gave me an overall ratio of 12.37. The original AD transmission was a wide-ratio 3 speed ending in 1:1. The T5 can be generalized as a slightly less wide-ratio three speed transmission with a fourth gear of 1:1 and an overdrive 5th (which could have been between .72 and .86).
This post began as a question about the NV3500. That is a different animal from the T5. It is heavier and the ratios are different. There are other variants of it (used in Jeeps). One is the NV3550 and it separates from the bell housing, but to make it compatible with the GM bell housing you must buy or make an adapter. In my opinion the whole NV approach is both costly and could be a challenge to find the proper rear end (with a 6 lug hub and the correct width).
