Hvac Issue...no Defrost In Defrost/floor Mode

[bosro]

Had the truck in for some oil leaks last week.

Noticed my feet were getting hot on the way home so tried to adjust temp but would not change,just blew hot air out of driver side stuff.

Passenger side worked as it should on everything.

Got home shut it off,had a cool one thinking bout it then went for a little drive.

Everything works as it should except when in defrost/floor mode it will not blow any defrost.

Full defrost blows as per normal and ac works,all other vents blow normal.

Initially I thought it might be an actuator issue but would I not have more odd stuff happening?

Now I think there might be something in the defrost ducting jamming it from going to defrost/floor mode but then it works fine on full defrost....

Anybody have any insight into how the flappers controlling airflow work?

Can there be something jamming a flapper in defrost/floor mode while still allowing full defrost mode?

BTW this is an 07 LTZ with the digital dual climate control.