I am all about fixing my truck myself but I think for the first time I am going to have to take it somewhere. :(

After I run it for awhile and come to a stop say at a light etc, the engine lopes while idling. It goes from 1000 to 500 and back up again over and over until I start moving again. Replaced the PCV valve and checked for vacuum leaks and could not find any.

Would a diagnostic be able to report what is wrong with it? And how much do you have to pay usually to get one done. THANKS!

Is the check engine light on? What year and type of truck? Have you reset the ECU?

If the CEL is coming on then take it to autozone. They can plug it in and read the codes for free. If there is no CEL, a diagnostic computer might not tell them anything anyway. But most places just charge an hours labor to hook up the diagnostics and run it. A little more info about the vehicle might help though.

It may or may not tell you.Some places can charge close to $100.Ripp off,but they got ya by the balls with this computerized SHIT!

Not knowing what type of vehicle you have, it sounds like the computer is searching for idle. A faulty MAP (manifold absolute pressure) and/or MAF (mass air flow sensor) can cause this condition.
Good luck.

Panzer Out

Autozone does it for FREE.