I have some questions about what might be killing my gas mileage. When I bought the truck I was averaging about 16-18 MPG and has steadily dropped down to around 13 MPG. I figured it was a combination of air filter and fuel filter. So I replaced both and still the mileage isn't too great. I noticed today when I walked around the front of the truck I can smell diesel, but there is no puddles or any obvious leaks. Any ideas on what I might be overlooking?

 

Right now the winter blend of fuel is likely causing most of your problem. It is a dry fuel and causes all of us to lose a couple mpg's. Try a good fuel additive, or some 2 stroke oil.
Look around the motor real good to see of your leaking anywhere around the filter, or lines.

 

What fuel additive would you recommend? I did notice though when I yanked my fuel filter it was completely black. Is that normal?

 

Black filter is pretty normal. I use PowerService, (white jug for winter, gold for summer), but Howes, FPPF, Amsoil, Lucas, are all good too. Just get one specifically meant for diesel. 2 stroke oil, or non-detergent motor oil, are OK too, but no ATF.
You can use a whole qt, but you only need about 1/3 qt per fillup, put it in first, then fill, so it will mix.

 

I know this is way off my original question, but a little while back I had to replace my governor solenoid and sensor in my 48re because it wasn't shifting right and my pressures were way out of wack. After I changed them out it shifted great for about a month and now it is back to shifting all weird again in second gear. Is there anything that these auto trans are known for that will blow that sensor if something isn't just right? I've checked all my grounds and the flat braided line coming from the trans to the body isn't horrible but is a little corroded could that be what is blowing that sensor or could it be more?

 

check the power wire from the a/c compressor back up to the harness, they have been known to rub through on the a/c lines and cause the computer to do some strange things, mainly shifting problems, there is also another spot to check and i believe it is on the trans crossmember or around that area, for rubed wires

for the milage... have you calibrated the speedo for the bigger tires? and is that the computer milage or is it hand calculated, winter fuel will lower the milage a bit, but these computer milage calculators can be way off, my brand new dakota has bigger tires, but is calibrated for them, but shows 12-13mpg's on the display, when it actually gets 17-18mpg's (hand calculated)

 

Remove and clean that corroded ground. The electronics are very touchy on those trans.

 

The computer tells me that I am getting 18-20 mpg and my hand calc is maybe 14 mpg at the most. Where exactly does that harness run to that you were saying rubs on the AC lines?

 

directly above (to the rear) of the compressor. (the power wire to the compressor)