Hello,as far as running, fuel filter or water in gas. Have you had the intake gaskets replaced? I have a 96 s10 with 130k. Had gaskets leaking leaking water into intake and out. Gaskets were ate up bad. Gas mileage went down when i quit feeding it water.
I have a 96 fullsize with a 5.7 also. PS Hey Zippy i had a 84. Problem with it was a coil mount to a rusty exhaust manifold. Would idle no mater where the throttle peddle was and not miss a lick. Needed a ground. I've been on the interstate berm for miles up and down hills at idle before i got that figured out. WTF Mike