Thanks so far guys but it passed a compression, leak-down, and vacuum test. I know about the exhaust thing but didn't realize how much strain I was putting on the valves by removing the Cat.

Though I mentioned the engine was rebuilt I don't want you guys to be mislead.....This was done in May/June and the truck has run beautifully since. This problem seemed to develope just after installing the new muffler.

As far as the exhaust is concerened...from the head pipe to the flex pipe, all is original. Then there is a straight pipe in place of the cat, then there is the new muffler and original tail pipe.

I left it at school where I have a warm place to work, plenty of tools/equipment at my fingertips, and the expertise of the instructors and seniors readily available.

I am still wide open for suggestions. The instructors have mentioned valves as a possibility but they are also thinking that it is nothing too serious and may just take some time to diagnose. At least I get lab credit for working on it but I'd much rather be driving it!!! <img src="/forums/images/graemlins/smile.gif" alt="" />