OK, I'm sure this has been addressed but here's my problem. I have a 2001 Dodge 2500, Diesel, Auto, 3. 54 gears. I recently serviced the transmission, installed a Transgo shift kit and used Redline C+ trans fluid. Saturday I was coming back from Albuquerque, NM in route to home, Cortez, CO. I was pulling a Carson 20" enclosed trailer that weighed between 5-6000 pounds. Heading west on I-40, into a headwind, but the truck is pulling fine. As I pull one of the many grades, the truck had kicked down into drive, I topped the hill, it shifts into OD lock-up and then within 1/2 mile, it shifts down into drive and my "OD off" light comes on. I hit the OD button a few times and nothing changes. A couple of miles down the road, it shifts back into OD and the light goes out. It does this a half dozen times between ALB. and Gallup. At one point, I'm driving along about 1800 rpm in OD lockup, I get into the throttle to pass some one, and major shudder. I get out of it immediately and all seems fine so I try again and major shudder again. There had been a couple of instances at the first of the year, pulling the same trailer, where I got a little shudder but got out right away. Since the service and Transgo kit, there had been no shuddering issues but I hadn't pulled much. We stop in Gallup to fuel and thats when I notice that there is no lock-up in drive or OD. Its shifting fine, just no lock-up. Tonite I take it to a buddys shop and he hooks up his Snap-On scanner and we go for a ride. The scanner shows no codes and according to it, all is well. Pressures, Temps, are good and it is showing that the converter is getting the signal to lock-up, but nothing is happening. We're guessing torque converter and I've been wanting to do the DTT stuff but you know how these things happen at the all the wrong times. If you guys have any ideas, I'm sure open for suggestion.