Re: 4.3 mods for mpg
Get a K&N filter. It's the best $40 I ever spent on my truck `96 with the 4.3L. It boosted power noticeably and I think MPG's went up a little.
If you've got a lot of miles on the engine, a new set of plug wires might help too. Get good ones (I like Accel wires), cheap ones are 'cheap' and I've had stock and inexpensive wires cross-fire and arc to the body in the past. New plugs won't add as much (~$6/ea - they are platinums in the Vortec's), and since newer engines run so lean anyway, the plugs normally don't foul out.
Low restriction exhaust will help some, too, but I think I listed the biggest bang for the buck above.
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