I have a 2001 dodge ram 5.9 off road edition and I replaced a bunch of parts and went from 5mpg to 10mpg but I feel like most people get 13-15

Heres what I've replaced:
- Both O2 Sensors
-TPS
-All new upgraded Bosch injectors
-Air Filter
-Coil
-Plugs, Cap, Rotor, Wires

I am also getting the P0455 code but would that cause the low MPG's? Anyone have any ideas?

 

You have a vacuum leak in the evap system, and yes, that may have a negative effect on fuel economy. Fix that.

What brand O2 sensors?

What flow rate on the injectors?

 

Bosch O2 sensors and as for the injectors I was told they flow 1lb an hour more than stock but they have 4 hoes instead of one for better fuel atomization

 

Honestly 10mpg probably isn't too far off if it's city driving. I mean my 5.9 4x4 is only rated at like 12 city as a brand new truck, and yours is an off road which means higher gearing (4:10's?) I can completely see you getting 10mpg with the 5.9 and that gearing with a ten year old truck. With that said, definitely fix the vacuum leak as that can definitely be hurting your mpg.

 

+2 for vacuum leak.

Also, Bosch O2 sensors are known to be hit or miss on quality. Denso or NGK are usually the way to go, for future reference. Cost a little more, but much better quality usually. Rock Auto has great prices on the Denso units usually.

 

+3, Take starter fluid and spray around each injector while running. If your truck jumps in rpms you found a leak. I had a leak in 2 of mine after I put the FI airgap and I gained a full mpg or 2 after fix.