I happened to check my rpm's @70 on the highway today just by chance - 2K @ 70 w/3.27's - That means your readings indicate closer to 4.30's, but at least 4.10's. Based on how short you say first gear is, my guess is that you've got 4.30's in there.
I think you should check your math. 1st on the T56 matches the 3650 with a 3.73 gear. The rest are all improved in terms of torque multiplication through the drive line.
I agree that any conversion to a T56 requires a rear gear upgrade to match the low gear performance of the 3650. What...