your tranny has colored gears, same as older ones.
I used the gears out of the 86 BW1350 I used for my doubler and swapped into the '95 trans case, they're the same.
4.88's with 35's is very close numerically to 4.10's and 30's, which i think you said you had before, I don't see how your speedo could be too far off, if anything try the next higher number gear.
I went from 3.73/ 29's to 5.13/ 33's, my speedo is about 22 mph off at 60. I need the highest tooth gear (21) but I don't think that will even get me close to actual speed. I have a 19 tooth gear now.
It should be closer when I get some 35's or 36's on though.
95 Ranger Super cab
Dana 44/Ford 9 SAS