my truck starts and idles fine,but drive it down the street and put it under a l

Hello, This sounds a lot like a vacuum leak. Smoke test the engine to see where vacuum pours out. If you find no vacuum leaks, let me know.

Here is another random -- yet valid -- thing that I have seen on these trucks: the PSOM (Programmable Speedometer Odometer Module) can cause running and operational concerns. Strange but true. Certainly check as per Casey's recommendation, but there can be some weird other things going on if concerns remain after verifying all else is OK.