I have a 2009 Yukon Denali. There is a small underscore under every letter from P R N D like this (_) and it'* not showing for some reason. When I place it on reverse the underscore goes under Manual (M_1) even though it'* on reverse and its takes the car a couple second to realize that it'* on reverse then it shifts with a slight jump to the back and the Stabilitrack light comes on! And when I place it on Drive (D) and go its really heavy and it drive on one gear and it does not shift or change gear! And when I push on the accelerator it goes to 3 on the RPM then gives out like if I released the accelerator even though I didn't!!! The only way to make it drive normal is to stop and turn the car off then switch the key a couple of times until the underscore (_) shows up under Parking ( P ) then I turn the car on and put it on drive and the underscore ( _ ) still showing under Drive ( D ) and the car feels normal and it shift gears like there was nothing wrong with it! But once I place on reverse it goes back to the same problem all over again, it shows the Underscore under ( M_1 ) even though it'* on reverse and it takes a couple of seconds to realize it'* on reverse and the underscore ( _ ) disappear and when I put it on Drive it does not shift and to fix the problem I would have to stop and turn it off and wait for the ( _ ) to show up again!
Please if you know what'* the problem with it, I would really appreciate your help!

Sounds like an electronic position sensor is whacked.
I would say that a shop scanner is going to be needed to read any fault codes.
If you could post back the codes, that would be great!

I will visit a shop as soon as possible and see if they could figure out what'* the problem or find out what'* the fault codes if there are any!
I didn't go to a shop and posted here because I wanted to know if there is someone who been experiencing the same problem or have fixed something like that before! Knowing that if I go to a shop most of them would simply say change the transmission like if it'* really simple or inexpensive to do that and the problem is way easier than that!