Hey guys, I've been dealing with this issue for some months now on the family's DD. Is there a good way to test for a bad torque converter, or if the problem lies in the transmission? The trans currently has about 260,000 miles on it. I rebuilt with new seals and clutch packs, and a new remanufactured torque converter at around 215,000 miles due to a broken sun gear shell. All was good until I was towing home a boat back in January. About 300 miles into the return with the load, the TCC had started locking/unlocking while at steady throttle and highway speeds, as well as a harsh 1-2 shift. It got worse up until the trip ended. We made it back, I researched all the threads and info I could find online. I replaced the shift solenoids, and accumulator, seemed to be the easiest fix. This solved the harsh shift, but after a few days of driving, the TCC lock/unlock issue was back. I think the fresh fluid suppressed the problem for a few days. The next likely suspect was a worn valve body valve.... which I had my doubts considering the symptoms came on out of nowhere. Seems like a worn valve would be a much more gradual problem, but maybe not. Check engine codes are P0B00 (auxiliary transmission fluid pump motor - phase u current malfunction), P1870 (transmission component slipping/transmission mechanical transfer case 4x4 switch circuit failure) Anyway, I installed a Transgo shift kit with the modified tcc valve to solve the worn valve issue, if present. I didn't touch the servo though, which the kit had different springs for, didn't think it had anything to do with the lock/unlock issues. After a few days, everything seemed good, so we took the boat up north, about a 4.5 hour trip. Shortly before our arrival, I could feel the TCC lock/unlock issue was back. It got really bad on our way home, to the point it was slipping so bad, it was always downshifting into 3rd, struggling, and we seemed to have lost 4th gear completely. Once we made it home and the truck sat for a couple days, I went out and drove it, and everything feels normal, shifts into 4th, etc, but the TCC lock/unlock is still present. I'm not towing anything until I know for sure it's fixed. Here is my dilemma. I can get a used trans w/ torque converter for less than $200, but I really don't want to ditch the transmission that I spent a week rebuilding if it's a simple fix which doesn't involve tearing the transmission apart on the bench. I'm starting to suspect a bad torque converter, but I really didn't want to just swap out the torque converter using trial & error, to find out that the problem lies in the transmission, and it needs to all be removed again for a different transmission to be installed. Is there any good way to test the torque converter? Any other suggestions on what to check/replace on the transmission to fix the TCC lock/unlock ussues?