My truck has emissions testing coming up soon and I still had GM's recall cards on my desk, so I finally relented and took my truck in for the recall work. Not sure about my state, but my research suggested that some states will deny registration renewal (CA for sure) if the DMV sees emissions related recall work not completed. To be honest, I also wanted to be on record as completing the recall and purchasing the EPA compliant tune.
After driving home from the dealer with the GM settings, I simply could not bear to drive the truck with the stock settings. I had forgotten just how soggy, numb and awful the stock settings are. The engine didn't even sound as good as it did before, the cool little intake hum at cruise was gone. Clearly my 2.8 was not nearly as happy as it was before I brought it in to the GM dealer.
Purchased and installed GDE's EPA compliant tune ($50 for prior customers, I elected to get the regen notification screen for another $25) and to be honest, I can tell no difference between it and their prior "Pre EPA" tune that I had before. All the same solid, immediate and linear response to any touch of the pedal is back, the quantity of power is back, even the intake hum. I would never be able to definitively tell the difference between pre EPA and EPA compliant settings. If anything, the latest settings seem a bit smoother at low RPM pulling a light load in a tall gear, but that is seriously nit picking. Any differences there may be on the dyno are not readily apparent in actual use.
Transmission settings were much the same, I was running the "09AC" file before, the latest approved settings are slightly more refined, but nothing drastic, a tiny bit smoother but in no way "mushy". I can't imagine a 6L50 trans working any better than this, as GDE can't do anything about turning our 6 speeds into an 8 or 10 speed.
So I have used GDE's pre EPA settings for 40,000 miles, the latest GM settings for 15 miles, and now GDE's compliant settings, so I can say from immediate experience what the differences are. At this point I dunno why GM does not pay GDE a bunch of money and simply use their EPA approved settings, as they are night and day better than the settings GM sends these engines out into the world with.
In their prior post GDE said "most likely, the bench calibration met emissions in the vehicle and not much more effort was resourced for drive ability characteristics". That is a nice way of saying that the stock settings are raw and unfinished, and no refinement or "fun" of any kind was baked into them.
For those who feel they "missed out" on the pre EPA settings, take heart, you really are not missing out. As far as the driving experience goes, all the goodness of the pre EPA settings is still there. I am shocked - really did not expect the compliant settings to be this good and yet they are just as refined and just as much of a kick in the pants too. Kudos GDE, well done