My 03 1500 4.7L only gets 12 mpgs highway. When I am cruising at 45 - 55 mph, When I hit the accelerator, my truck will not move until I hit the accelerator enough to kick in the overdrive. So basically I can only accelerate using overdrive. What can this be? I changed the plugs and the fuel filter. Took the air box off and drove like that... nothing.. No codes come up either.

 

Could be the torque converter...that would explain the bad mileage also. Check your tranny fluid and make sure it's at the proper level..

 

OK, will do. I'm not that good with these things, so can you explain the function of the torque converter (in a nut shell) so I know.

 

It could also be your cats. I have seen them get clogged and really takes away the power.

 

thanks a lot. Would the cats being clogged throw a code?