we had a big gmc truck intoday. 90 tbi 454 2 ton dump. ran o.k. but loads up bad when first starting up in mornings. kind of doggy on power. we checked all the comon stuff. but we traced it down to a bad egr valve. get this the pintle was gone . whent someplace but its not on the egr anymore. funny thing was the whole time no codes or check engine light. priced a new one for the guy and thay said 120 our shop cost and not in stock ord item 3-4 days. guy said i dont care just make it run better. so we fired up the welder and filled the pintle hole shut. made a diffrence. so just a helpfull little story for ya to keep a eye open for.