the most important factor is your driving style, i get 260 miles on 11 gallons, 89 2600i. with even with the tires the gearing they brought it right back to stock, the speedo and odometer match up with gps. but i also hardley ever let it get over 2500 rpms before shifting it and always run it as low as possible. i know of alot of people with 5 speeds that leave it in 3rd because they are doing 40 miles an hour = horrible mileage

 

Amazing! My truck, 90B2600i extended cab 4x4 with auto, will barely go 200 miles before fill up time. I just replaced the head and am runningGeneral 235/75-15 Grabber AT2s that were installed a few months ago. And a new OEM type Bosh Oxygen sensor. It starts and runs perfect so I should be happy and I am but the mpg!! [:@]



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That's horrible! My stock 84 B2000 get's around 250-280 on a tank...

 

With all this work done have you done a compression check to ensure you are within wear specs, sounds like low compression could be causing lack of some power and the engine is working all the time instead of just maintaining the work load. Also sounds stupid but any loose feul lines? (not meaning to insult you)

 

Did a compression test before I replaced the head. Number 3 had low compression by both dry and wet test.Turned out to be a crack from number 3 cylinder exhaust value seat area to the gasket surface. The other cylinders tested in the 180psi range.With the new head there is no oil consumption or smoke when first started. I regularly look on the underside and under the hood for anything that might be dripping or leaking. So far everything is dry including the fuel lines. The truck only has 125k miles but I think I will do another compression test to elimnate that possibility.Also no error codes are being generated by the ecm.