Difference in trans = better milage
MoparPat -
The final drive gear ratio in both the 904 and 727 trannys is 1.00, so no difference in RPM at 70MPH in 'Drive'. However, the 904 has less HP loss due to lighter internal components.
The standard gear ratios for both the 904 and 727 are as follows:
904 trans
1st: 2.70
2nd: 1.54
3rd: 1.00
727 trans
1st: 2.45
2nd: 1.45
3rd: 1.00
The only way to lower your 70MPH rpms is to go to a higher rear gear or install an overdrive trans.