When the Obvious Is not so Obvious
We had a 1995 Ford Super Duty with a 7.3-liter diesel engine and E4OD transmission that had no trouble codes but appeared to be going in and out of TCC lockup at steady cruise speed. If you accelerated hard when this was going on the TCC would engage properly until you came back to cruising speed and there was no more load on the engine. This was a commercial truck that had a heavy air compressor in the back and was always towing a big trailer, so the problem was very noticeable as the truck was being driven.
