Gents I've resolved the issue. Well actually you guys fixed my issue and i just turned the wrenches.
It was 1 of two issues - most likely both.
I ruled out tires and rear shock angles as well as the droop settings. I've moved the shocks back to the factory set up specs and the ride height to 10 mm.
Here's what I did change that appears to have resolved uncontrollably loose condition.
1) the extreme RC mods pipe makes massive low end torque. I swapped the pipe to a Novarossi super strong EFRA pipe and I went to a whopping 20/24 pinion. LOL On cold tires the modded .28XZ still has enough grunt to break traction but when the tires get sticky it hooks and the torque has no problem turning the massive pinion. My straight away speed after shifting to 2nd was a crowd pleaser!!
2) I have eaten much crow in my life and will do it again here. After listening to all the advice here AND spending hours researching scale race car theory I added rear toe back to the car. On corner exit I believe the decrease in bottom end torque and the modest rear toe setting is keeping the rear end under the car and pulling forward.
My Kyosho GT2 with custom OFNA rear end has zero toe and it hooks up BUT I will concede that i was wrong by applying that set up to the shorter/much more powerful Serpent. The rear toe on this particular car appears necessary.
Can't thank you all enough. Parking lot racing with my new hot rod is fun again.