A week after buying my '98 Silverado w/145k miles at a dealership, it started running rough through the entire driving range. Pretty irritated at the dealership, but ya know, "AS IS".

Tried the fuel filter - that wasn't it.

Anyway, bought a set of plugs (just Autolite Plats) and started removing the old ones - turns out the old ones were AC Delcos with normal wear but were VERY ready for replacement. Not sure how many owners the truck has had but I'm willing to put money that those were the original AC Delco plugs New plugs made ALL the difference, guys. Runs PERFECT now.

Sometimes (THANK GOD) it's the simple fixes.

 

Great!