a few weeks ago i changed my plugs, plug wires, air, and fuel filter on my 90 sierra 350 tbi. it ran good and even got 18 mpg. then 2 weeks later it started running really rough at cruise speeds. when i am at a steady speed just giving it enough gas to keep the speed it cuts out and is really rough. then when i park it and try to start it immeaditatly it wont completely turn over. it just cranks a little then stops. ive asked quit a few guys and no one seems to know. please help.....

your problem starting sounding like what I've currently got on my 96 350, 4L60 half ton. I changed the plugs before going on a 1000 mile round trip. After a couple of days of local driving after getting back, my truck started hesitating at cruising speeds. I've been testing it and it seems to do it only when the tranny is in overdrive. I added a transmission conditioner and have run it for around 50 miles. It has gotten better, so it is leading me to believe the tranny is getting tired. I've got 145000 miles on it so I guess it's about time. I do change the oil once a year and it is time to do it again so I'm gonna try that first.

What throws me for a loop on your issue is the hard starting after it is warmed up. It will probably be a sensor that is going out and gets worse once it heats up. Those types of problems are a PITA to troubleshoot. Good luck.

well... thanx for the reply... i really hope its not my transmission. it only has 30,000 miles on the rebuild. i took the truck into my transmission man and we put it on the computer(it was free computer use from him) and it said i had an egr problem. there was a broken hose running to the egr so i fixed it and it didnt get better. we put in on the computer again and it didnt say anything... maybe i fouled a plug? im slowly singling things out. good luck with urs. again thanx for the reply.