I found a list online of a company auctioning off trucks and it had vin numbers listed. That was how I found the 01. From what I've found, 1500's were 4.3's, 2500's were still 6 lug, but had the 5.7l up to 02, 5.3l after 03, and the 3500's kept the 5.7l through 07 classic and all I've seen were 5 speed manuals. It took me weeks to find that list, but they were all 3500's and up. Still looking for an 02 2500 with a 5.7l auto to see what GM did differently for them. The only difference's I seen in the 01 was the maf scaling since the gmt-800 trucks use an 85mm maf vs the vans 75mm maf, and the VE table was a good bit higher all around(not sure if this was due to the different intake, larger maf, or that they're tuned to run on leaded or unleaded fuel).