What was the rpm? Might it have been lifter pump-up. Your description of not" happy after that" kindof points in that direction.
50mph with 25.5s and 3.23s would be about 5500 with a 904
273 solid lifters, 2.93 rear ratio, 25.8" tires, 1st gear to 40mph = 3840rpm, 2nd gear to 70mph 3978rpm I don't have a tach so the numbers are calculated.