i jsut did the calculation. i'm getting 21 MPG with a 8V stocker. only extra is 235's. but veeryone with 31's or bigger are getting atleats 25 from what i ahve read. any suggestions? new exhaust, bosh o2 sensor, cleaner galore through her. anythign else? i kwno somoen told me osmthign befor but i can't find my old thread 

Im getting the same milage (bout 20 MPG, maybe a bit more)

I just got used to it..  I did the exhaust, plugs and wires and none of that helped a lot so,, I learn to live with it.

here yah go

http://www.zukiworld.com/forum/index.php?topic=13632.msg125507#msg125507
http://www.zukiworld.com/forum/index.php?topic=10961.msg103742#msg103742
http://www.zukiworld.com/forum/index.php?topic=11884.0

Remember when you increase your tire size you are traveling farther than the odometer and speedometer indicate.  I went from stock to 30" tires and with stock I was reading 30mph and on radar actual speed was 29 and now on the 30's I read 30 and on radar I am going 32.5mph so that is a 10-12% change.  Therefore mileage will look worse for my new set up when in fact it hasn't changed at all. 

I know one thing that would help me and that is get my overdrive (auto trans) to kick in at 40 instead of 49mph.  I drive most of the time at about 40-45 and the overdrive doesn't kick in as much as it could.  The difference is over 500 rpm at the same speed and that would make a great difference in my case!  Everyone I talk to tells me that the factory overdrive settings cant be changed and I have posted before on the topic and no one had a way to change the setting.

DW has an important point there.

You can further check it out  without a RADAR gun by driving around with a GPS receiver turned on in your truck.  Once you have put, say 100 miles (161Km) on the truck - or some other semi-large easily-rounded number - you can calculate the overall difference between the odometer and what you actually drove as indicated by the GPS's Odometer reading (most GPSes have an Odometer mode).

Once you have determined the odometer difference, you can (if you want) take your truck to a speedometer shop and have an adapter installed to correct for the tire size change.
 
A GPS can be handy for other stuff (geocacheing, position locating, street navigating - although I think that feature is overrated...) so a purchase of even a cheap GPS might be a good idea instead of a speedometer shop correction.  Plus, if you change tire sizes again, you don't have to buy another GPS receiver!

So beg, borrow or buy a GPS receiver and calculate your actual speed/MPG!

Does anyone know if a calculator exists that can calculate how off the odometer is.  I added 31s and was wondering this to calculate gas milage.

Thanks