it can be used "On top" of a tuner. It doesnt re program the computer like a tuner does, it "Lies" to the PCM. So you could use it on top of a tuner. Im going to bet most tuners would tell you not to. Id be looking for this on a stock application with maybe a cold air and exhaust. I dont think id go throwing this on top of a custom tuned truck with many mods. Just my 2 cents.
There is no reason to use it with a tuner since the stock computer can command as much boost as go want. I am very curious about this.
I want to tune my truck but I can't afford to ditch the warranty right now. I have heard that for warranty claims the truck ecu has to be downloaded and the info sent to ford. So there is no getting around it if the computer has been flashed they are not gonna cover a catastrophic engine failure.