Z28 Muscle

Having an odd problem with my transmission: the aftermarket torque converter occasionally decides that once the coolant reaches the temperature at which the torque converter will lock up (first notch on my temp gauge), and the converter locks up, shortly thereafter (within a minute) it will unlock, causing rpm's to shoot up, of course, and highway driving to become most undesireable. After about two minutes, it will lockup again, then a minute or two later, it unlocks again. This cycle repeats all the way to work in the morning (about a 20 minute drive, all expressway). At the end of the shift, eights hours later on the drive home, it once again warms back up to 'lockup temp', locks up like normal and never unlocks the whole way home. I seem to only have this problem in the morning, usually before noon, and some mornings if it's mild outside, it won't do it. I'm assuming it's something in the computer right? But I can't decide what's tripping it to unlock: temperature in the morning? Humidity? It used to only unlock while I was cruising between 40mph and 60mph (over 60mph it would never unlock), now it seems to do it at any speed over 40mph (speed at which it locks up). Anyone with knowledge or advice, please advise...

The car is a '99 Z with a TCI 3500 stall, headers, and 3.73's.