I'm thinking yes, yes sir you may be right sir.

I love my truck and I'm having lots of fun. It's a fun truck, but someday I'm going to get a nice 2500 with Hemi and just drive it

 

I don't have an exact weight on the OE aluminum 20" rims but I they are very light. I will try and find the weight. The rim mfg for your 17's says they weigh either 34 or 35lbs depending on which exact 17X9 you got.

I got the weights for the tires though( TG AT's not MT's )

P305/50R-20 = 49lbs each
LT295/70R-17D = 65lbs each

Depending on the weight of the OE rims you may have added weight going to these 17's but it won't be a lot. The tires themselves weigh 16lbs each more. So 64 lbs extra weight with the tires. Not enough to have much impact weight wise even if the rims weighed the same.

I would say what really has hit your MPG is the tread on the new tires. You said the old tires had very little tread depth left. So, going to new tires with such an aggressive tread could take upwards of 2 MPG off your average. I bet this is where your biggest MPG loss came from as I suspected originally.

 

That sounds like good intensions. But in reality I'll bet right now that it won't last long. Once a modder always a modder.

 

That's funny because after I wrote that I thought "well, maybe just rims and tires..." LOL

Which I know leads to other mods. I would at least drive it stock for a little while.

 

Yep, same thing I said.

 

Ok, another tank of 89 octane and now with the CAI installed..... <drumroll>

.... 12.56!

Oh wait, that is a reduction. hmmmmm

 

I used my GPS to determine the odometer is 4.3% low. There is no adjustment in the computer for tire size in an '03. The door placard will advise the stock tire size. I suspect it isn't 33". My 285/70s are only 32.7" and they're a good deal larger than stock. I get just under 15 mpg (corrected and properly calculated) running 80 on the interstate.

I suspect the mileage has suffered to some degree due to the "motor-music" the Magnaflows are providing.