Duke72

Hey all I'm new to the forum and to Chevy's. I bought a 98 Z71 about a year ago that had 198,000 miles it now has 210,000+ and runs good except for my Service engine light.

Here is the first problem the light was on when I bought the truck and the dealer read it as Catalytic converter so I took it and had 2 Magnaflow cats put on and they cleared the code. I drove it for about a month and the light came back on. I took it back and they said it was calling for the cat. again so they cleared it and I drove it for a week and the light came on again took it back now it is O2 sensor. I replaced all 4 sensors drove it for a week light back on check it Cats. clear it and drive it for a day or 2 light comes on again now calling for cat. and 2 evap codes. I finally set up an appointment with the dealer so I can find out what is going on once and for all since inspection is coming due. I went out this morning and temp. was in the 20's and no light!!! Drove about 20 miles and still no light after being on for nearly a month now I make an appointment to get it checked and the freakin light is out.

My second problem was this summer anytime it was warm to hot outside and I would drive anymore than 50 miles straight without stopping the truck would fall flat on it's face anytime you would get on the gas. I made one trip to SC about 4 hours one way. I left early in the morning and the truck ran fine all the way there but about half way back it just would not run. When I say would not run the truck cranks up and runs fine but it just has no power. For example merging into traffic onto the highway running say 40 MPH on the exit then mat it to merge and it just won't go it just falls flat on it's face. I have not run into this problem since it has cooled off so it has to be heat related but can't tell if it is fuel system, ignition system or what.
Thanks for any help
Duke