Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
I would be more inclined to expect an end clutch issue since they are pretty well known for failure on this model, and the front clutch and end clutch are the merging elements going into 3rd gear.When the shop rebuilt this transmission did they take it apart and replace worn components or did they do an actual overhaul replacing all wear components and not just what looked out of sorts?
The only real expectations for difference between hot and cold is with the expansion of the fluid. Obviously the fluid being low would have been noticed already if that were it, but also the grippiness of sorts of the frictions will increase as the fluids warms too.I have heard of people doing that with the fluid to warm it faster, but honestly if the unit is built 100% the problem won't occur. These didn't slip when new, it isn't a design failure but rather a component failure. That said... if you are OK with something like that its certainly cheaper than anything going internal of course.
I think at this point the best thing to do beyond the obvious of course of double checking the fluid level is correct and resetting the TCM (unhook the battery and hold the cables together for a few seconds), I would be doing a line pressure test before going any further.
If you find the front clutch or end clutch pressures are lazy to build (both should nearly instantly go to 120 psi when the shifting to 3rd "begins"), then we would want to pull that valve body out and check for any irregularities, and if nothing is found then a full tear down to check all sealing O rings/D rings as well as checking the back plate for wear on the transmission.
If the pressures build instantly like expected, then we would consider a possible friction issue (perhaps the end clutches needed replacement and were not changed, or the front clutches were changed but plunge depth was not set correctly) or at very last resort a TCM issue. It pains me to even say that as it is so rare, but specifically these 2G Spyder TCMs are beginning to show some strange traits as they are getting on in age now.