I'm not 100% sure but at 80MPH, your car is going up against a fair amount of wind resistance. The amount of power required to accelerate or even maintain speed goes up exponentially as you go faster.
Even with 0% WGDC dialed in, your car will still develop wastegate boost at that speed due to wind resistance and other things related to physics. It is impossible, without physical modification of the car, to make the turbo generate 0% boost under throttle at that speed because the load on the engine is high enough to cause the turbo to generate boost. And because it's a feedback system, it's not possible to open the wastegate to bypass the turbine until you're generating the required wastegate boost. Get it?
COBB does have an economy map that does kill off the boost as much as possible, but you'll hate yourself for running that map because it'll be slow as hell.
Control your foot, ease off the gas, you should be fine.