Gas monster

Hi my truck is roening me on gas cost its a d200 -68 whid a 400 bb 727 11" turbine shift kit dana 60 stock ratio ported stock heads headers Eddy singel plane intake holley 600 vac carb 68 main 4.5 power valve new proform ign set at 18 in 42 total no vac no pinging stock pistons low comp i think the cam is the Akilles heal have no specs but sounds nasty in idle suspect its a 268 or 272 comp cam but far from shore runs realy good lots of power iv made a 100km run onley hiway 55mph average 2.2l/10 km no load just me and the dog thats a lot in my book what to do

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