4 spd. pops out of gear.

From what I can see, the sync's look like new, and don't see anything out of ordinary. Another thing I didn't mention earlier when I commented is runout. I have taken transmissions apart that were said to be rebuilt, and found the thrust washers not installed correctly. Reach in and grab the lower cluster gear and see if there is movement back and forth. If the trust washer came out, due to not being installed right it would definantly cause grinding, and mis-alignment issues. As I stated before, popping out of gear is generally a worn key or broken spring issue, but it's impossible for me or anyone else to troubleshoot this without taking it apart and seeing it in person. Also, stick an extension magnet into the oil in the case and see what shows up, that's how I've found missing thrust washers before, they will raise hell with gear boxes if they get into the gears.

Jeff