i have a 2005 chevy lly my mpg went from around 19 to 20 down to 17 mpg. i used to get about 100 to 110 miles before i cam off of full. but now it is barely hitting 75 or 80 miles before it comes off full. what could be the cause of this. my driving habit is the same

Fuel filter, air filter, bigger tires, tire pressure, oil change? What are your mods?

banks six gun tunner with speed loader., afe mouth piece, banks ram air box, ppe ported rail fitting, ppe race fuel valve, bd-manifold, de down pipe, 4 inch mbrp exhuast, south bend clutch. 2005 chevy 2500hd 4wd single cab long bed. 6spd manul trans it is riding on 33x12.50R20 tires. it has ben on 33s for about 2 yrs and the mpg was 20 to 21, but it is now at 17 to 18 mpg and the tunner stays on level 3

summer fuel?

has to be it. i hope it gets better. but i am fixing to do more modds ina few weeks.