wanting to buy a tuner for my stock 2008 2500hd d-max whats the best one

mostly using for towing/gas mileage/and some times for a little more power

The million dollar question. The most common are Edge Evo, Quad, PPE. The best i say be EFLive but comes with no tunes. You tune it yourself or purchase from tuners.

All the above write to the ECM and if needing warranty work like an engine or transmission issue you would more than likely be denied warranty work because of the altered non stock ECM tune.

Brian

What are you concerned with? Keeping your warranty or tuning? How much do you want to spend?

warranty for sure but need more power and better fuel mileage

If you need a warranty then your only options are Banks or Edge Juice with Attitude module systems. They plug in and alter the signals between ECM and engine. But if you say run the Edge on level 6 and smoke the Allison the TCM will have recorded data that will indicate high HP and Torque applied to it. So when you remove it and take it in they will know something is up on that. All the others I listed above alter ECM tune and is trackable. The ECM records the last 10 different tune calibrations. One single change in a stock tune creates a different calibration number. recommendationAlso if you think of a DPF delete the only way for that to not code is a tuner that alters ECM tune. So the module systems will not work with DPF deletes.

If you need a warranty then leave the truck stock is the best recommendation.

Brian

so you are saying if i buy the edge or the banks and not run it on level 6 then i should be fine for warranty they can not track the other levels.just want to make sure.
i more or less want it for better fuel milage

No thats not the thing. If the module over does the Allison even on the lowest setting it can be said that there had been a programmer since the ECM knows what it puts out and what it sees based on the modules making the changes but the TCM sees the real output and it does not match. Running level 1-6 will eventually at some point slip the Allison. Like I say nothing out there is not traceable. Even if it can be removed. More power over stock causes faster wear and tear.

Brian