3sp vs 4sp isnt an option.... the 4sp is the same almost as the three speed in 2nd 3rd and 4th.... think of the 4 speed as 3 speeds with granny low.... in other words second on the 4 speed is about the same as 1st on the three speed,,, same with second and third.... get it..???? so if ya put the three speed in it will still labor in 1st.... so if ya dont like the way it is changin the xmission wont do it.... its more the rear end and if you go with an overdrive then ya want the 3.90 probably....or it wont pull it in overdrive on a hill or headwind without labor the heck out of the engine....goin fast anyway....
