1999 Suburban with a 5.7 VORTEC. It'll run just fine for 20-30 miles or so and then suddenly sputter and die. Tries to fire again when you crank it but usually have to wait about a minute or so and then try again.

The truck had sat for 4-5 months, had about 5 gallons of old fuel in the tank which I burned off a couple gallons and put 5 gallons fresh in there to dilute the bad stuff.

When it happens it almost feels like an exhaust restriction. Since it's intermittent I figured it wasn't a plugged Cat. Do these have an EGR valve? Can anyone tell me where it might be and how one might clean that if carbon is built up in there?

Thank you.