GPS was acting weird today. Made a flight almost to Elko but saw the weather deteriorating and decided to head back rather than get stuck by trying to get a meal in the casino. On the way back to SLC it started acting funky. Just west of Wendover KENV it started having trouble with altitude. I'm crushing level at 9,500 and the GPS would swing from 12,500 to -1,800 ft msl. I didn't know the Garmin Pilot had an excessive sink warning on it but after having it go off four times today I do. Halfway home the course started displaying irraticaly and the graphical track would spin. The Notam period for the testing hasn't started. We have good visual references around here so it's not that big of a deal but it just goes to show you to keep sharp using the old standby methods.

Rich