I searched and found nothing on 3rd & 4th lock-up, only 4th gear lock. Maybee someone can help me with this. I have a 86 700R4 that was rebuilt before and they hacked up the wiring so there was no lock-up. The last rebuild only lasted 10,000 miles! This is going into an 86 truck that will do some towing, so really my question is should it lock in 3rd gear as well as 4th? Most towing is done in 3rd gear, not in overdrive. If ther is no lock-up in 3rd will the tranny overheat while towing a load in 3rd? Thanks!