those 5 spds in the troopers had about the same problem with the 5 th gears as the pickups did , however i have seen many of them go 150-200 thousand miles if they are serviced regular, another problem with the 5spd in the dsl was most people would drive around in 5th gear at around 45-50 mph around town driving and it was just too much load on those small 5th gears , as 5th gear is a remote gear in the trans and in the 4spd 4th gear is a direct gear , being that you have The front and rear diff from the 81 which are 4.11 just put these in the trooper, just swap the frt and rear diffs and use the 4psd with the 15 inch tires from the trooper and you should be good to go ,finding a good used 5spd for one of the troopers is pretty tough , as most of them have made the 150 thousand mark who knows , the 5 spd internal parts are almost identical parts to the 4 spd , it is the indirect drive of the 5th gear setup , however most all 5spd boxs are that way , the cheepest and the easiest and most durable way go with 4.11 frt and rear diff and the 4psd ,, and the bigger tires JERRY