3g hemi gas mileage

I just ordered a set of gauges from Speedhut. Ordered one of their GPS speedos, can't wait to get back on the road. I called them and grilled them about reliability with the GPS unit and they said they have sold 100s of them around the world and the only time they don't work is when you are in a tunnel or underground. And one fella had a problem when he mounted the reciever upside down under his hood wtf?