I have an 81 1/2t 4x4 with a 350 and 3.08gears.I am running 31s.I put a rebuilt q-jet on it as well as a new complete distributor with a performance module.Cruising on the highway the vacuum gauge reads about 10".I can get up to about 13" but any wind/slope will drop it back,sometimes down to ~5".When I accelerate or pull a trailer there's a point when black smoke comes out of the exhaust.I use this truck on the highway and am looking to increase MPG.I know these trucks aren't known for fuel economy but I'd like to get it as good as possible. My timing is set at 8deg and I have 18.5" vac at idle.
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