Monty

You can use it both ways. But, I think it is primarily used when a truck will not start and isnt throwing codes or will not start after the engine is up to operating temp. Which are both signs of a failed VP. Basically all it is, is a breakout harness that eliminates all of the electronic signals running to the VP. You can build your own if you can find the 7pin VP44 plug. Just wire it on the constant power terminal (#6 I believe) of the VP plug. We have one that we have built at the shop I work at, but hardly ever use it.

My first guess would be to check the lift pump pressures at idle and cruising speed. Most of the time a low power complaint can be traced to this. However, some have found that there low power complaint was due to the TPS out of calibration.

Amish hauler

I agree about resetting the "apps".(accelerator pedal position sensor) I have to admit it sounded kinda wild to me when I first heard it. But I was at the same point you were...either spend $1800. for a new pump or try this for free. This time the free trick worked. It seems when I replaced my batterys something got out of whack. Try it it won't hurt. I've also heard a dirty IAT sensor (intake air temp.) will have the same effect. And just to clean it with alcohol. I would try both these before I would buy a non-returnable pump.