Why dose my truck sound like a valve tapping?

This is a problem that requires seeing and hearing the vehicle, and possibly tearing down the engine. Is the oil pressure OK?

Definatley low oil pressure to the top end of the motor. the pick up screen in the oil pan is too small (OEM)and gets clogged with sludge every 60K or so and the only way to clean it, replace it or fix it is to drop the oil pan, In the 4.2 you gotta pull the engine to do it. Its a pain but it could fix the problem. id replace the main bearings anyway, your already 800 in, another $70 while the motors out BFD. I would also consider replacing the oil pump. clean all the valleys with a pipe brush. I found that a couple rocker arms are slamming the tops of the lifters, which is causing the tapping. Not enough oil going through them push rods to keep it pressurized. i cannot find a high volume or high pressure oil pump anywhere for this motor, they only make them for 5.0L or bigger. strictly a V8 part. Sorry for resurrecting a 5 year old post.