Attention: TDR Forum Junkies 
I have this theory about tuners/programmers, and their effect on mpg. I believe that they fool the in cab mpg display to tell you that you are getting better mpg, when in fact that isn't the case. I have spoken to numerous people, and read numerous posts on internet forums (this one and others) where owners claim significant gains in mpg when using a tuner or programmer.
Also, most of the manufacturers of these devices use that fact as "testimonials" to sell their product. In order to prevent themselves from getting into any "jackpots" over false advertising claims, they usually craftily word the ads like; "Our customers report a 2-6 mpg increase when using our tuning!" and other such claims.
I'm here to tell you it just isn't the case - at least not to the extent they'd have you believe.
I tested a Superchips programmer for mpg improvements on my previous 2002 Dodge/Cummins Ram, and now have tested the Hypertech Max Energy on my 2007 Dodge/Cummins Megacab.
On the 2002 truck, if I drove easy, in the lowest power setting, I noted a 0. 5 mpg improvement from stock. In the higher 2 settings, I lost mpg. That truck DID NOT have the in cab mpg display.
In the 2007 (which I just filled today), the overhead computer (which I had reset on the last fill) told me I was had got an average of 21. 4 mpg on that tank on my daily commute. When hand calculating distance driven over gallongs used, I actually got 18. 5 mpg (50/50 city/hwy) - a 3 mpg overshoot by the in cab display.
Also of interest is that the effect on my Scangauge II is even more dramatic. It has me at 30+ mpg most times on the hwy.
When the weather warms up again, I plan to compare the lower 2 settings to stock on the Hypertech to see if there is in fact any mpg increase. I don't have the amount of data I would like to have before saying yes or no, but it is interestingly possible that I may be gaining a tiny bit of mpg (nothing close to 3,4,or 6 mpg though). Stay tuned for that in the spring.
I'd like to point out that I'm still happy with the purchase of the Hypertech programmer, as this is what I was expecting to happen. The power increases are still there, so I prefer to look at it as increases in power, with no penalty in mpg - the best of both worlds.
Also, most of the manufacturers of these devices use that fact as "testimonials" to sell their product. In order to prevent themselves from getting into any "jackpots" over false advertising claims, they usually craftily word the ads like; "Our customers report a 2-6 mpg increase when using our tuning!" and other such claims.
I'm here to tell you it just isn't the case - at least not to the extent they'd have you believe.
I tested a Superchips programmer for mpg improvements on my previous 2002 Dodge/Cummins Ram, and now have tested the Hypertech Max Energy on my 2007 Dodge/Cummins Megacab.
On the 2002 truck, if I drove easy, in the lowest power setting, I noted a 0. 5 mpg improvement from stock. In the higher 2 settings, I lost mpg. That truck DID NOT have the in cab mpg display.
In the 2007 (which I just filled today), the overhead computer (which I had reset on the last fill) told me I was had got an average of 21. 4 mpg on that tank on my daily commute. When hand calculating distance driven over gallongs used, I actually got 18. 5 mpg (50/50 city/hwy) - a 3 mpg overshoot by the in cab display.
Also of interest is that the effect on my Scangauge II is even more dramatic. It has me at 30+ mpg most times on the hwy.
When the weather warms up again, I plan to compare the lower 2 settings to stock on the Hypertech to see if there is in fact any mpg increase. I don't have the amount of data I would like to have before saying yes or no, but it is interestingly possible that I may be gaining a tiny bit of mpg (nothing close to 3,4,or 6 mpg though). Stay tuned for that in the spring.
I'd like to point out that I'm still happy with the purchase of the Hypertech programmer, as this is what I was expecting to happen. The power increases are still there, so I prefer to look at it as increases in power, with no penalty in mpg - the best of both worlds.
