[comptiger5000]

I've got a 46RE (same ratios as 48RE) and 3.73, so the only gearing difference between yours and mine is the tire size. I know mine will climb a hill and have enough power to just start to gain speed before I hit the downshift point in OD locked at 1100 (36mph, any slower and it unlocks the TC). It's good enough to have surprised a few people that it did that and isn't a diesel.

I could probably lug it down to 800 locked up on the flats at 30 - 40 mph. I wouldn't want to go below 1000 - 1200 on the hills though.