This issue has been going on for a good year now. I have replaced the opti, plugs, o2 sensors, plug wires, and icm. I have no codes and fuel pressure is perfect. I just recently got it dynoed and got 234 at the wheels. I'm pretty sure there is something wrong with her because I get about ten miles to the gallon and when I'm driving it I let off the gas and it boggs down and sometimes backfires. I even went so far as to take it to the dealer to see if they could find anything in the pcm that could point me somewhere. They said the tune looked good and couldn't find anything. The mods I have are bbk headers true duals k&n mad opti 4.10 and a tune. Any advice or anything I can check? Could it be a clogged cat?

 

sounds like a weak valve spring or a couple cracked ones...do a compression test and confirm...sometimes you might be able to catch a cylinder bleading down if you are unable to do a leak down test as well..if all confirms to be good...

 

Ill do a compression test tonight and inspect the valve train I also wanted to add that the hotter the car gets the more rough it feels idk if that would help trouble shooting or point to something else

 

well then...what i said might not even be relevant to your problem..although it wouldn't hurt for hindsight's sake..

sounds to me something might be heat soaked?..