Mitsubishi Repair: 2000, Lancer, 1.5, GLXi, Auto, wagon, torque converter, intermittent problem

Question
I have an intermittent problem, i start out driving, about 30-40 minutes into a trip i pull up at traffic lights, they go green I start to accelerate, it goes 1st to second fine, but second to third it kind of stutters, it attempts to go into third but drops down to second again and repeats the process 3-4 times sometimes, it will do this for a couple of stops at traffic lights and then it won't happen again for a while. it seems to happen more often on hotter days. The only code it came up with was for gears not synchronized.

I have had the gearbox rebuilt, it seemed to fix the problem for a couple of weeks, then it started happening again.I took it back to the transmission place, he checked for computer codes and it came up with nothing. He is at a bit of impasse, has no idea.

So what is going on? Have any ideas? Is there anything I can do?

Answer
Daniel,
You should have the torque converter and transaxle control unit inspected.  It could also be the transmission fluid cooling lines are clogged and the fluid is getting overheated.  If your mechanic has not checked those items, have them look it over.
Good luck!