screen resolution problem on 3GS

Hi folks. Hoping someone might be able to help with this.
I was running the Tom Tom app (plugged in to a Tom Tom cradle) arlier tonight. I closed the app when I arrived and then I switched off the car and removed my phone from the cradle.
Ever since, the screen keeps switching from the native resolution, to some wonky res that does not fit on the screen. Kind of like running the wrong res on a monior, where you need to mouse past the edge of the screen to make it move.
It fixes itself up if I open certain apps (phone) but as soon as I open ANYTHING else, it craps out again.
A soft reset has not helped.
Anyone have any ideas?
Your help would be greatly appreciated!