Toyota Repair: 1996 manual transmission pops out of first gear, nylon bushing, steel balls

Question
At 125K miles my 1996 tacoma 3.4L V6 5 spd tranny started popping out of first gear.  I held the shift lever in first accelerating from a stop on an incline and killed first gear.  I replaced the tranny (with a used one) along with the clutch and it still pops out of first gear.  I replaced the nylon bushing on the end of the shifter and it still pops out of gear.  I have one more dealer order bushing to replace - cost $41.  I see references on teh net to ball & spring (3 of them) that hold the tranny in gear.  According to shop manual diagram these are called "locking balls."  WHAT ARE THESE FOR AND IF I REPLACE THE SPRINGS WILL IT FIX MY TRANNY PROBLEM?  My local toyota service advisor has never heard of the springs/bearings.  Thanks,  George

Answer
Replacing the springs will not fix the problem, you need to replace the shift bushing in the top of the shift tower
the one that needs to be replaced is about 1/1/2 in" diameter, have the parts department look it up for you, just replacing the teflon bushing at the end of the shifter doesn't solve this problem.
The shift interlock steel balls,pins and springs DO NOT prevent the transmission from popping out of gear, all they do is to prevent the transmission from being shifted into two gears at once, don't waste your time replacing them. Service advisors know very little about how everything works so I'm not surprised at your comment.
Replace the bushings that the parts department ordered and see if it fixes the problem, let me know if you need more help