On a 727, shortening the cable will hold it in gear longer before it shifts. I don't know if it's the same for 904s or not.
When I installed my Lokar, we took all of the slack out of the cable and tightened it down. After a couple hundred miles, it started shifting funny, so I checked the cable. Sure enough, it had stretched just a little. Took the slack out of the cable and it shifts fine again!!
