Transmission problem? '02 Kia Sedona 3.6 V6 85k miles.

About 3 weeks ago, while driving out of a parking lot, going maybe 15 MPH, car pulled back (THUMP sound and feel) suddenly and ck engine light came on. Car was not shifting properly. Drove home (4mi) and left alone until next am. Car drove fine, engine light still on. Drove to my mechanic who pulled a trans code (0200? Something to do with the Output -or was it input?). He did not clear the code since still under warranty. Made appt next day w/Kia dealer. Next day, ck engine light off. Dealer ck'd and found no problems. Drove fine until last night.

Same problem (and happened at practically same location - will explain later). Drove home, ate dinner. Needed to run errand, so drove it around block (after about an hour of rest) and car drove fine. Ck engine light still on. Drove this morning. Uneventful. Ck engine light finally went off at around 5pm, almost 24 hrs since problem.

I have no clue what the problem is, but I am sure there is one. The 2 times this has happened to me have been after about an hour long drive home from work where I p/u daughter at school and bring to soccer practice. Car sits for about an hour. Both events happened right after soccer practice. The 1st time I was only pulling out, maybe going about 15 mph. Last night, I was cruising down the road for a minute or so, doing about 40-45 mph when car pulled back. The problem with the gears seems like I have no 1st gear (maybe 2nd).

Can anyone shed some light on this? How can the dearler find NOTHING? Not even the code, which, as I said, was NOT cleared. Shouldn't they have seen that?

BTW. Car has been serviced (timing belt, tranny flush, filters, fuel injection flush, oil changes, etc).

Sorry so long.

Thanks for reading.