I have noticed a decrease in fuel mileage i have owned my dads old truck for about 4 months now and i always thought he got about 18 and i did all my mods and i now get around 14-15mpg and before all of mods i got 16. There is a "Thonk"

when i press the breaks and it sounds like it is coming from the passenger side front wheel. So what i was thinking is maybe a break is hanging up and thats the reason for the poor mileage but the thing about it is, is there is now smoke or hot smell coming from the break. any advise