popping out of 3rd

I had it taken apart for that reason, but when it was apart 5th syncro was out and nothing was wrong with 3rd. So 5th gear parts were replaced. Its a pro 5.0 shifter. He said if you dont use the shifter and just use the extension to shift it, that it would stay in 3rd, but when he put the shifter back on it pops out. Im hoping that its the shifter. Hes getting a shifter from a t-5 and putting on it to see if it still pops out with it on there.
 
Why in the hell did you fix 5th gear synchros only? You should have A) rebuilt the entire tranny or B) put in a completely new one. I mean, fix everything while your in there. It looks like you'll need a complete rebuild now. I would just buy a tko....