In the 2003 48RE is the torque converter supposed to lock up in third gear when the OD off button is engaged? Mine seems not to. When towing at lower speeds (below 60 in the hills) and locking out OD to keep rpms up the trans temp goes up.

 

My '03 with a 47RE locks up in 3rd. After dropping out of OD try easing up on the go pedal a little bit and see if it won't lock up for you. In 3rd, the lock up is very subtle and you have to watch the RPM guage to catch it. Only about a 100 RPM difference sometimes.

 

Mine locks up in 2nd at around 30 (I think), 3rd at exactly 50 and OD at 55 depending on engine load. Seems to be consistent towing or unloaded.

 

Thanks for your replies. Going to the dealer next week for differential fluid change. Will have them check out the torque converter then.