trans slipping out of overdrive

when driving normal i get up to about 50-55 and the converter locks and if i slow down to about 45ish it will all of a sudden kick out of overdirve and rev high and not really go anywhere then if i let off and hit it again it will lock up and be fine. one does it when im at part throttle. wot its fine shifts beautiful no slipping at all. i wasnt going up a hill or anything to make it downshift. it did it 4 times today. im thinking the converter is going. truck has 136k on it and i doubt any tranny work was done. right now its deleted with IDP xtreme street tune. i rarley drive the truck and when i do i dont really beat it bad at all. im hoping its something electronic telling it to down shift. thanks guys

Check for codes. Sometimes a CEL won't come on

Checked for codes and nothing come up. Checked both engine and tranny for codes

This doesn't sound like a TC issue to me. If it was it would slip locking up the converter or slip while the converter is locked

I'm thinking it might have just been confused, it happened when it locked up and I would slow down to about 45 and it would just seem like
It downshifted too far. It only happed when I was at a certain position with the throttle so it may have been right between where it wanted to down shift or not