Self dimming mirror issues

Ok, I've had this truck about a month now, and already have 4000 miles. I run alot of evening calls for work, so I'm out after dark quite a bit.
I kept thinking that the self dimming mirror really wasnt dimming all that much, so I started investigating. If it werent for the rear tinted window, it wouldnt be worth a shit!

So according to the maual, there are 2 light sensors, 1 front, 1 back. When i'm on country roads, it seems to work just fine. When I'm in town with street lights it doesnt seem to do much.
Tonight, I had to run about 40 miles on the highway, and realized that if my GPS is on, it creates enough light to un dim the mirror.

My plan tommorow is to put a piece of elec tape over the front sensor to see if this helps. (it says NOT TO COVER THEM)
Am I being anal, or does anyone else notice this. I thought about calling dealer, but I'm wondering if they have any way to really test this thing, especially during the day.

 

I dunno about you, but with my canopy on, that's a total of 3 tinted windows between my mirror and the headlights behind me, so I don't notice any change at all.

Maybe it's just that in the city, your eyes are adjusted to the ambient light, so you don't notice the mirror changing as much as in the country?

 

mine doesn't seem to work worth a damn... let us know how the tape idea works out

 

I don't notice any dimming on mine either, I wish I just had the trusty old tab on the bottom to switch it back and forth, lol, at least the tab works