Does anyone have any issue running Performance tuners on the 6.7L Cummins?
1. Has your fuel mileage improved? If yes by how much?
2. What warranty issue have you had or engine problems such as Turbo failures and head bolt issue?
3. What turners do you think are the best? Such as Banks, Edge Juice,Bully Dog and Quadzilla?
My son feels that the Smarty is the best one but when is this tuner going to reach the market, if ever.
I am looking for ways to improve the fuel mileage not necessary  more horsepower performance, the 6.7L has enough horsepower now. I have read were most tuners state that they will improve mileage but that's the "ADD men" talking. Real word data is best.
Thanks in advance.  

If you're going to go with a tuner that what you need to do is one of these two things.  Go with either a pressure box thats undetectable or go with a Modular Tuner such as the smarty (when it comes out) thats undetectable.  Most of the pressure boxes I have seen all are undetectable.  You simply plug it in under the hood in the proper spot and then you're good to go.  Those all work on timing.  

The modulars is what you have to look out for because they flash the ECM and a dealer can detect this.  The only one, that I know of anyways, is the Smarty.  This is the most versatile tuner on the market for the Dodge Cummins.  Diablo Sport however, has a VERY good performance tune that can enhance power but give you good economy it gives you 100hp and 180ft lbs.  I ran this with diablo pressure box, a intake and a CFM plennum, put a torque converter and valve body in there and I was getting 25 miles to the gallon, that was with 15000 miles so it wasn't even broke in.  The thing is is that the modular will most definitely be detected.  But see I wasn't worried about the warranty stuff.  If you do it right and don't run the piss out of it.  You're gonna outlast that warranty in know time so yeah.  

As far as Turbo failures.  You won't have any turbo failures unless you over spinning your turbo.  I good safe point for your turbo would be 30-35 psi for stock.  Thats if you want it to have good reliablity and long lasting function.  A good upgrade you chould think of is a boost fooler, it tricks your ECM into thinking thats it's consistantly running a certain PSI when in all actually you are getting 10+ psi out of your turbo.  The reasoning for this is that if you draw more boost then what your ECM will allow, then you're truck will instantly go into defueling mode.  If you get to 40psi then you're gonna need Head Studs,  anything above 40 psi you could possibly lift the head gasket then you will have to put head bolts in it anyways.  

What I would do is this.  For economy, get a boost fooler.  Also by a intake and a CFM manifold.  The CFM will not void the warranty, the intake will but you can save your stock and when you need to go to the shop just slap the original on.  Next By a pressure box thats undetectable and get a modular thats undetectable.  Only run them on the performance and not balls to wall.  Also buy a torque converter and valve body.  With what you're wanting to do, these two upgrades alone will enable your tranny do withstand around 550hp which is really good for the dodge, those will be the only upgrades you will need with what you're wanting to do, maybe a deep tranny pan too just to keep things cool also.  

Also, but this would void the warranty.  If you can get a DPF kit with a delete file.  I would put a straight 5 inch all the way back.  I hear that you can see increases of 4 to 5 mpg just on the upgrade.  I am not for sure what they have for the dodge but yeah.  I have also heard of people developing and fabing the piping so that when you take it back to the shop you simply take you piece out and slap the converter and DPF back in, but you will need a 4 inch for that.

If you did all those things there is no reason for you to be in the 20's it would be easy.  I would estimate that you would be in the 22 to 24 range instantly. The only thing is that DPF, because the DPF is a very big road block right now for economy on those newer diesels

But anywho hopefully I helped