Whats wrong with my 4l80e???

got a used tranny and its been a pain in my a$$ ever since i got it. its a 4l80e 4x4 and recently i can be doing 50 down the road and after 15 ish miles the torque converter will unlock for no reason and just stays that way. once that happens shifting becomes rougher, but if i pull the truck over and shut it off for like 10 seconds and restart it and take off everything works fine... kinda stumped anyone have anyideas what could be wrong??
i bought a brand new converter from monster transmissions when i put the tranny in 1000 miles ago, 1400 to 1600 stall. running dextron 3 fluid and tranny cooler

Check for any dtc's even if the light isnt on.

Check the temp of the trans fluid when it does that. An infrared temp gun would be helpful, just shoot the bottom of the trans pan. A lot of times when you have hard shifting its tied to a bad TPS or a short in the TB harness at the TB.

sorry to sound dumb but whats all those mean lol i dont know squat about trannys.

Whats a DTC allen??

and whats a tps throttle pos senser?? or a tb ??
thank guys for the help.
is it possible to over heat with a cooler if theressome thing wrong with te tranny itself?? ithink i have a 10 x 15 inch cooler.

also on my first tune you did allen we tried the retune because of the shifting porblem. but when we did the retune the shifting never changed... it was the exact same bfor and after . so maybe i have a shift kit or a rebuild is in order... its just been problem after problem with this thing!!!