MPG Motor Magnum vs. Hemi

After I had installed the res.valves I noticed the front wheels where always hard to rotate by hand when jacked up.
Too hard to be 'right'. Now that I removed the front res.valves again I notice just a slight drag just a like any other car has.

My mileage ranged between 10 and 11mpg. Around 9.5 with the front residual valves installed.
Mileage is always worse in wintertime, better when the weather warms up. But this spring I didn't notice the mileage improving again when temps went up, which let me to suspect the brakes.

Mind you, I'm running LPG / Propane.
CompCams XE256H
Always drive fairly short 15-30 minute trips. 60/40 highway/city.
A518 transmission - 8-3/4" rearaxle w/3.55 gears.