I am getting codes P0172 and P0175 and it seems to me as though I am going through gas quicker than usual. Recent transmission replaced with one that has 15k. I have also noticed that my speedometer is showing how fast I am traveling. But, where you can see trip info this is showing incorrect average speed. when clear I can be going freeway speed and it reads in the 15-23. No, this is not reading the mpg I am wondering what would be causing this and would that have anything to do with the codes?
Appreciate your help, thank you.

 

forgot to add 99 XJ8 thanks again.

 

P0172 = System too rich (Bank 1)
P0175 = System too rich (Bank 2)

This seems to be a different issue than the tranny issue, but it sure would cause lower MPG.