I really don't trust the TPS. When I had my '07 and switched wheels and tires for winter/summer, it took the truck at least 20 minutes of driving to realize there were no sensors in my summer wheels.
Were your summer wheels in the back?
I did notice a similar issue with mine after I removed the wheels and drove away from them on the wheels without sensors. The readings when I checked were ---, yet the alarm didn't go off for a few minutes.
So, in the absence of sensors, it reacts differently than it would for a sensor that was showing decreasing pressure. The alarm goes off quickly when you are getting a flat. This I know for a fact.
