Real MPG experience with 5.3L (TH350 and/or NV4500)

[Aruba1]

I am looking for some input in regards to the MPG for a stock 2000 5.3L Vortec engine running standalone (EFI) with 4:10 ratio.

The 5.3L is bolted on to a stock TH350 in the donor truck. I am debating between running a TH350 or a 1997 NV4500. The former would be an easier swap because I will just leave the old one in place and bolt the engine to it. The NV4500 is more work because I need to install a high hump floor and do some fabrication. I have all the necessary parts to do either install (special flywheel, clutch, etc).

My main question is towards MPG. What are you seeing with a TH350 or a NV4500 and what gear ratio do you have? Please limit discussions only if you have real experience with either swap.