transmission

[714x4lover]

i have the 4 speed with granny tranny, i can never remember the name of the dumb thing, its very common, has the two pto side plates and it s in my 71 truck. my ? is ,is there a tranny thats a direct bolt on maybe a little modifacation, that has the 5 speed mine runs at 2850 @ 65 3000 @ 70 to 75 mph, if there is, what is the name of the tranny? are they rare? are they expensive? are they heavy duty? just want to save a little on gas, plus im gonna put a tpi to help with the gas problem also./ any help would be great.