Try to make this short. Bought a 94 K1500 with 190k on original motor in good running order. Did a complete tune up, fuel filter, NGK plugs, wires, cap, rotor, blaster coil, regapped plugs, synthetic fluids, ect. Ran like a top and increased my mileage to an average of 16mpg which I was very happy with. Unintentionally ran it hot and cracked the block one day. Finaly got a remanufactured short block, not a gm crate and installed my old resurfaced heads and dropped the motor in. Broke the flat tappet cam in and got the valves adjusted correctly it now runs like brand new, it seems. I'm on my 7th tank of gas with about 1,300 miles on the new motor and I have gotten about 8mpg on each tank. I babied the last two tanks and brought it up to a whopping 9mpg. WTF. I know new motors will tend to get better with more miles but everyone I talked to said it shouldnt take but 1k miles. I know people don't like anything but AC Delco parts so I will buying new AC Delco coil, plugs, wires to try that. But how did i manage to get 16 with an old motor and my exact setup then drop a new motor in and get half that... Any ideas???