I have a similar setup on my LML. I have a 5 tune pack with autocal from PPEI, EDGE CTS2 and Pyro probe. I have a few more items installed as well. As far as the tunes go, I am happy with them. I run the 60 HP tow tune all the time as that is pretty much all I use the truck for. The truck does smoke a little if you get on it to pass someone but clears up once the turbo spools up (within seconds). In regards to their support, they are a little hard to get in touch within an hour of quitting time, but other then that they are more than willing to help when you are on the phone. I did a lot of my communication through email and usually got a response the same day.
In the end, there are quite a few reputable tuners for the DMax and I don't think you would have heartburn over going with others as well. I chose PPEI at the time I was looking at tuning my truck, but I wouldn't hesitate to go with some of the others either.
2015 Chevy LML 2500HD LTZ CC/LB
14" Duraflap Mudflaps
ICI SS Running Boards
Bushwacker OE Fender Flares
Northland Aluminum Front Bumper
EDGE CTS2/EGT Probe
MBRP Downpipe /5" Flo Pro Exhaust
PPEI ECM/TCM Tunes
Airdog 4g 165 Lift Pump
Deviant EGR Plates/Merchant Auto PCV Reroute
295/55R20 Toyo MT's on Stock Rims/Height