If the tune up doesnt help with the mpgs, I would look into a high flow cat or gutting the cat you have, if the cat is going bad it will hurt mpgs

 

The smallest tire that Dodge put on these rams was a 245/75-16....

 

The one inbetween the 2 02 sensors? I gotta cut it off and weld it back on correct?

 

Yeah the catalytic converter(cat) is the one between the 02 sensors and some people cut them off and take a bar and knock all the insides out and weld it back in or clamp it, if you have emissions you will need to put a cat back in

Also when gutting cat you are at a chance of getting a cel there are a couple tricks to fixing this main way to do this is non-fouler trick

 

I guess the tire calc has some bad info.

at a 245 stock size, with 265's
Speedometer Difference: 5.844% too slow

http://www.1010tires.com/TireSizeCal...?action=submit

 

i know its off the topic, but do you idle at 650 rpm?

 

Yup. why?

 

I am pretty sure the other guy posting in here is correct that 225/75/16's were used on some 2wd's which would make them the smalllest. Let me look around and ill get back to ya.

Edit

The FSM does list a goodyear tire that was offered in this size. Tire rack lists the 225 & 245 sizes. My truck came with 245's stock and listed 265's as option (which I had installed last summer). To clear any confusion, OP would you mind snapping a clear pic of the sticker in your driver door and posting back? Thanks

 

My silver truck originally had 225's on it.

 

My door jam sticker lists 225/75/R16's as my stock size. Wether it left the dealer lot with these on I have no idea. Mines a 4x4 too.