I have a 1997 cummins 2500 automatic that use to get 22 MPG but now only gets 13 and 14 on a good day. What's going on? Also could it have anything to do with the transmission?

 

welcome to db
did you do anything to the motor recently to affect the mpg?
we are going to need some more info on when it started dropping, ect.

 

The truck is practically stock with no mods to the motor, over time it has just got worse. Lately it seems the transmission is not working property, could that affect MPG

 

Very much so.

 

How do u turn up the boost on my 98 12 valve cummins?

 

[QUOTE=Bruiser Dodge;1094313]

How do u turn up the boost on my 98 12 valve cummins?

 

I would start by having the Injection Pump timed .. they can over time slip ..

also run a quart of ATF ( dextron .. not synthetic ) .. it will help clean out the injectors and combustion gum.

also Fuel pressure and the trans will KILL your Mpg ..