[USSkoval]

Two things, the first being very important.

1. Get the lock up working!!! You will overheat and kill the tranny with it disabled. Overdrive also isn't as effective without the lock up.

2. If you are going slow enough that the engine is lugging, it will likely help to drop down a gear. Next time you are driving 55mph in OD, without moving/changing the accelerator, drop down to drive. If the truck starts to go faster, then it is more efficient to run in D.