Are my stock pipes too restrinctive???

Your good and your pipes aren't stock anymore.

Most people don't realize a modified engine can breathe easier create more power and be more efficient. A gas engine is the least efficient out there, a jet is one of the most efficient. Stock motors are built to meet epa requirements not reach there full potenial or anywhere close. You throttle dictates how many miles you get per gallon Stock engines that are run wide open right off the line and thru the gears will get much less than one feathered off the line and the throttle used just enough to get the job done.