I had just bought mine recently and after doing a little research on her I found out that the vortec is a 200 horsepower engine which you got to admit aint bad but mine was running sluggish also. I wasnt throwing no codes just didnt have the get up and go it should have expecially going up hill. Had a good friend tell me that these beasts are prone to having clogged catylitic converters, went ahead and bought one new and you wouldnt balieve the difference, like night and day. I dont understand how it would have a huge impact on the engine but its doing alot better now. Worth a try to give it a check...