Well last wk I installed my 50 series Flowmaster HD and removed the resonator and install a K&N cone filter within the factory air box and remove the snorkel also and its like a custom job thing. I did go a bit crazy last wk on enjoying that way it sounded. Oh i also installed a optima red top battery so of course I had to disconnect the battery. So I put 10 gallons in on sunday on a empty tank and Ive been driving normal and I mean normal so like 55 on cruise. So how long will it take the ECM to learn its new breathing levels. Im showing 11.4 miles to a gallon and before I did everything it was showing 13.4. So how long before it starts to hopefully show the correct gas mileage. ALSO when your gauge says you have ZERO miles before empty do we still have like a gallon or less left.