Slipping Transmission on Old Truck Slipping Transmission on Old Truck

Q. I just purchased a truck. It is a 5.7L V8 (350) Automatic Tran with O/drive and towing package. The guy who owned it before me got rid of it because the engine was making noise. He thought the engine was going to blow any day. But with one belt and an idler pulley, it's as good as gold. Except for one thing. When I am driving on the interstate, about 65-75 mph on a flat even road, with the cruise control on, the transmission feels like it shifts in and out of overdrive. I can't really feel it, but I can hear it in the engine rpm. The truck has 175,000 miles on it, so is the transmission going, or is there something I need to adjust? When I stand on the gas, the transmission downshifts properly. I haven't noticed any slipping or anything like that, just the overdrive problem.

A. Go and have the truck scanned for codes and data, and also check fluid condition. 65-75 mph is the mark when overdrive is just about to engage. You might find that differences in weather, like a strong headwind would lock it into overdrive at this speed.

You should also take the truck into a transmission shop and have them test drive the vehicle, as the problem may not be transmission related. It could be an engine misfire, which will often feel like the transmission is shifting in and out, and commonly may be mistaken for a transmission problem. The problem may also be with the converter, and how it locks and unlocks. It may stay locked driving with a load, while it locks and ulocks without a load. To fix this problem, you would need a valve body modification.

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