You could go with the discrete GV unit that could be mounted between the transmission output and the rear differential, if there is enough length (more likely a possibility if yours is a long wheelbase truck). It would have a short u-joint shaft between the transmission and the GV, then a one-piece driveshaft to the diff. Do you have a two-piece driveshaft now?
Or you could go with a late-model manual transmission with overdrive.
