My service engine soon light has came on for the 2nd time in 2 months. Both times I was passing a car on the highway, around 75mph, and then the light came on out of nowhere. The first time I went to autozone to get it checked by the computer and it said "random cylinder misfires" the guy didn't know anything about cars, he couldn't even tell what kind of truck I have, but he said the best thing to do was to
take it to a shop. I took it to the mechanic I normally go to and he said my spark plugs were too weak and to replace them. I replaced the sparkplugs, wires, and distributor cap and everything seemed fine, until today, I was passing a semi and the light came on again and i don't know what's causing it. Can anyone help? I have the 5.0 v8 with 140k miles.

 

You have to read the codes again to see if it is the same cause.

 

Lots of those Parts Pushers don't know what code means what, but...
It's nice that they'll find out what codes are shown, and you can write um down. There's several lookups on the internet, and you can go directly to the GM site and chat or find phone numbers for a direct talk about your problem.

Chat site:
Lemon Law Concerns | Car Warranty Laws & Repairs | GM.com
or
Direct lookup:
GM General Motors OBD Trouble Codes

 

The first code was p0400 I think, it was random cylinder misfires.
I went today to autozone and it was p0350, I think, but it was misfire in cylinder 5