The early 5-speeds are the most in depth install. They have the most parts you have to deal with.
The only set that I installed that had a similar issue was when I was doing a '97 and I had the wrong shift fork. It had very similar issues. Its been a while, but I'm pretty sure you need the -4 shift fork.
In any event you are going to have to pull the t-case. It isn't too bad to work on while it is in the truck.

1987 trooper LS.'94 3.2, SAS,35's , lots of dents and rust. Now, improved, with more dents.
1995 trooper LS. Wife won't let me improve this one.
1996 trooper. I'll need something to modify when the '87 finally rusts away.