[Fan of Fiat]

I had a Garmin Colormap years ago and sent the unit back 3-4 times because it would work for 5 - 10 minutes, then say I was driving at 400MPG and eventually lose signal.

Finally realized it was the CD player in my Dodge Dakota causing the interference.

Not a problem since.

[CPOSharky]

...I was driving at 400MPG and eventually lose signal.

You get 400MPG? ;-)