Your point is valid about waiting for GDE. If I had my '18 Denali in my hands, not sure I'd be waiting any longer either!
I don't know tons about these modern computer programs but what your saying, I don't feel is the cause of the over-boost situation.
The reality is that 99% of tuners shut off some codes, advance the timing and add pw to make the power. Sure they play with other things such as turbo vanes but it's not a surprise that since they don't monitor turbo speeds (like GDE does) and that since all the exhaust restriction has been removed, that you have a turbo over-speeding. They know that the manufacturers build a lot of safety factor in to these vehicles so they can afford, most of the time to over-speed the turbo a bit and run the egts too hot.
GDE has a totally different approach and this is why they are my only serious consideration for tuning. They have not released their tuning because the software available does not have the ability to alter pilot injections and other things that they manipulate. GDE focuses on reduction of C0 output (that's mpg) within the published safety factors (Cylinder Pressures, turbo speeds, egts) of the components being used. This also has the net effect of extending the lifespan of the OEM emissions equipment to beyond the useful life of the vehicle itself. They essentially do exactly what they do for the OEMs, but with a different set of priorities that consumers demand.
~ take care
Current: 2009 Canyon CC I5. 180K miles. Best vehicle I've ever owned.
ORDERED: 2018 Canyon Denali Diesel 4x4 CCLB