earlier this year, i swapped my fourth gen over to 700r4,)2.73 gears, first and second were amazing, but fuel mileage went way down, 60 mph was around 1100 rpm, (so lugging in fourth at 55 gets old) swapped to 3.73 gears and have never been happier, really woke it up! now with a tbi 350 i get 22-25 mpg around town and way better on the highway.
2.56 gears might not be so bad, but thats still pretty high for an overdrive.
the only things i had to change was driveshaft cut 3 inches, moved crossmember back and drilled new holes(90s blazer trans mount) and on mine had to change kickdown bracket(although it would have been as easy to change kickdown cable instead but i already had the other bracket.)