[Jac Mac]

There is a possibility that the detent springs for the 1/2 & 3/4 selectors inside the box are tired or not tight enough to bring both those shafts back to the exact neutral position when you cross over the 'gate' during shifts. These are the springs behind the 9/16" bolt on side of trans & under the top cover of the trans. The one under the top cover..there has been two versions, one that is preloaded with a 'phillips' head grub screw & the other is simply a longer spring.

Now the spring under the top cover is the detent control for 1&2, so if you 'adjust' the preload on that spring be sure to check that you can still shift that 1/2 action freely.

The detent for the 3/4 shift is under the 9/16" bolt on the side of the trans case, you can make up an adjustable setup for this one by using a longer 3/8" UNC bolt & nut and adjust the spring preload accordingly, again while shifting the 3/4 motion to ensure its not too tight......... Once you arrive at a suitable preload I would suggest that you cut a bolt down to the correct length & fit it, If you leave the 'bolt/nut' combo in place sooner or later some expert will tighten or loosen it & either lock it in gear or make it start jumpin out of gear...