Not directly, but I suppose you could say that it does affect milage indirectly. Say you start your truck up cold everyday and let it idle for ten minutes. If you have the high idle feature activated and it's cold enough to trigger it everyday, then you are idling your truck at 1200 rpm for 10 minutes vs. 800 rpm for 10 minutes. Running at 1200 rpm, the engine is going to use a little more fuel than the it does at 800 rpm. Since your not moving to rack up any miles, you can see a bit of a difference in milage depending on how long you let it idle.

Other than that scenario, I don't see how it could otherwise affect anything else.

 

Maybe I missed this, but is that feature only on 2001's? How much does it cost to have the computer re-flashed? Can Cummins do it or is it part of the DC computer that is be reprogramed?

 

All 24 valve engines can have it enabled. It is suposodly allready activated on 03 and newer trucks. My dodge dealer said they would do it for $40.