There are input and output speed sensors for all 4l80e. Eventually on 4x4 applications gm started using the sensor on transfer case for output. On a 91 4x4 truck, there are three sensors: trans input, trans output, tcase output. The shifter shaft location on a 4l80e also does not line up exactly in the same spot as 700r4. Not sure if will be an issue or not, as the shift linkage is frame mounted on squares. I don't remember from my 91 factory 4l80e square if linkage was slightly different or not.