Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang
 

All this time, money, effort and blogging about transmissions and adapters and you will still have a 3400 RPM motor. The finished product will not do anything a stock GMC won't do except wear out your right arm and left leg. Which will at least cost you your deductible.
If you are after mileage, it will take 10 years to recoup the cost of the mods with fuel savings.

Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang
 

Maybe, but with a train of thought you mentioned, who would be driving a classic car/truck in the first place? No offense meant.

I do think the V6 will benefit from better gearing compared to say, an SM420. The gears are just too long and the engines do not like to rev.

Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang
 

I just don't know what problem people are chasing.

Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang
 

That's a no-brainer. A wider gear spread for better take off speeds when pulling a light load, and milder highway cruising rpm for better fuel efficiency. Lower RPM on an engine that makes its peak torque at 1600 RPM, basically 1600 to 2200 RPM cruising speeds, will reduce wear on the engine as well, and the engine has plenty of grunt to push the taller overdrive gear. These engines' max horsepower is at 3600 RPM, peak torque at 1600 RPM (352 Magnum at 1400RPM!). dropping 530 RPM at 70mph highway cruising will really help out with fuel economy, and going from a 3spd or current Saginaw 4 speed 1st gear of 3.34:1 up to 3.83:1 will really help with better takeoffs especially when pulling a utility trailer or enclosed trailer with dirtbikes and motorcycles... I don't think I could get better than 17 MPG driving very conservatively on the current worn out Saginaw transmission. I think I can get 21 or 23 MPG with the ax15. Both figures are regarding the 351C engine swap. I have squeeze 21-23mpg out of the 305D. Pulling a utility trailer though (& 640lb Harley FXR), it was a max of maybe 13mpg. I think the 351C will do better mpg when pulling the trailer due to more torque, and lower RPM on the AX-15 as well. I have a transmission with a worn out synchronizer and some slightly worn bearings, so upgrading to a really nice condition $300 AX-15 plus the adapter plate and drive shaft shortening, is a big bonus. This fixes problems on multiple levels.

Re: 5 speed/o.d. swap comparisons - WC/S10 T5 hybrid, NV4500, A833 MY6, Tremec 3550 Mustang
 

Casey, would you mind if I gave you a call? I'd like to talk through your swap and get an update on how you like it. I will also send you a PM.