Wierd converter problem

[87gninpa]

I had issues witht he TCC when i first got the car this summer, so it was replaced and everything has been fine for the past 6 months. Now, all of the sudden the converter does not seem to want to lock allt he time. the chip i have usually lock it around 45 while cruising, but lately it has been going up to almost 70mph before locking. also, it unlocks sometimes when ont he highway at about 60-65 mph. Just wodnering if anyone would know a cause of this as the TCC has been replaced and the trans seems fine otherwise