OK, so the meet is over. There were two other Mavics there. Both were using Apple devices. Both were most current app and firmware. Both could hit 4000' with no warnings or glitching.
I asked one of them for thier iPhone so I could try it on my controller. With it, my MP flew 4400 feet before the first hint of signal issues. That ruled out any hardware issues on my MP or RC.
I put my android phones back on and once again couldn't get past 1000' before signal loss.
I thought great, now I now need an iFruit device. But with both Android phones behaving exactly the same way, and with most Android users having no issues with signal, I thought it can't be that.
Then I had a (very rare) stroke of genius... I asked if either operator still had their Android mini cable/adapter. They did. I hooked up my android with the new cable, and PRESTO! I had full clarity and signal all the way to 4500 feet.
Upon closer inspection of my original cable I could see where it had been pinched repeatedly between the phone holder arm and the body of the controller. What looked like scuffs was actually crush marks. The insulation was split on the edge and I'm sure the conductors were compromised.
TL;DR - if your having signal issues check your cable for damage. If you don't see any, replace it with a standard cable (using the bottom full size USB).
God am I relieved I don't have to start a DJI repair order!