1981 k5 w/'78 35O/TH350 Grr I'm just having one of those days. I get pulled over today, the truck I was going to buy has a bent frame, I found out that my whole tailpan is rotted out on my '81 and I got sold the wrong parts at the store. The thing thats really pi$$ing me off is my truck is running like $hit. When it gets warmed up it starts to bog out and loose all guts in third gear. It kinda feels like someone dropped half the clyinders or cut back the fuel. The wrong part I got was the fuel filter but when I pulled it looked pretty clean. If I drop it into second and rev it up and throw it back into third it runs fine. It'll do it if I'm crusing and have to slow so it goes to second and then I speed up and it'll do it as soon as it shifts, even with mild acceleratoin. Even when I gun it right of the start it'll be fine for a little bit before it dumps out. I don't if this helps but the transmission is freshly overhauled and the truck has worked fine for 2 weeks after I got it running after sitting for over a year.