Well if the EGR checks out with a vacuum pump before id replace the CAT id check the vacuum solenoid for the EGR and check the EGR tube itself along with the intake to see if anything is plugged. The only other thing it could be is carbon build up in the cylinders.

 

even after a tune up my truck was still barely not passing. Probably due to the intake manifold gasket issue... I cheated the test by pulling the vaccume hose going into the manifold. the rpm bumped up to around 1300 or so which is optimal..
passed fine

 

What is "VP"?

 

google say: http://image.chevyhiperformance.com/...ne_booster.jpg that, lol. dunno if it's the same thing

 

Sorry about not being specific, VP is a race fuel, meant that when you add a high octane fuel, the combustion or gases are hotter thus acting like a cat converter.

 

Okay, got the cat changed yesterday. They told me to drive it about 50 to 100 miles then bring it up there. So that's what I'm doing today. Yesterday after they changed it, I could tell a significant difference in power and how the truck was running. So I'm praying this is the problem and it's been fixed.