i opened that back i heard the blow motor worling and theres also a resister there..i dont see a blend door actuator like on older tahoes in the back like older models..just blower n resister..i wemt brought brand new blend door actuator and put that in by gas pedal..but still no luck with top vents ? Anyone point me in the right direction?

 

In my '11 there is a mode actuator in the rear blower housing.

 

I dont see nothing on mine..i think i got a leak in mine..blow way 2 much air on the wall side behind this part..

 

This is 2013..no sign of blend door actuator..

 

Alldata shows it in the blower housing on my '11 short wheel base and in the LWB it would be at the duct split. Looks like you have a shorty. Don't know what changes they made from '11 to '13 but take a look at the back side of the blower housing, maybe they moved it.