I have a 2003 dodge ram hemi 2wd with 113k mi on it. 5 spd automatic. I just changed the spark plugs a few hundred miles ago & it helped a little. I am currently getting 15-16 mpg on the fwy on Premium gas, and 13-14 on regular gas. 12-13 mpg in the city on premium & 10-11 city on regular. I have tried "fuel system cleaner" additives in the gas tank with no improvement. I am not sure what to do. I know Hemi's aren't good on gas but as far as I've read I should be getting better than what I am now, and at the very LEAST able to run 89 octane instead of 91. Please help me!