98 firebird question

I have a 98 firebird 3.8 v6. My air and heat work but it will only come out on the floor and the dashboard. Is it a fuse, relay, sensor, anything like that or something worse?

I want to try a fix that so I can sell it. I hoping that you guys could get me started with a base price. Its got almost 91,000 miles on it but the body is in almost perfect condition. Washed thoroughly every week, inside and out. The transmission was just rebuilt about 12,000 miles ago. The windows are tinted and I have a $200 Sony head unit that will stay in it. It also has a Flowmaster exhaust and the engine is maintained regularly.
Thanks.

Fixing your hvac problem means digging into the dash as all your flaps in your heater box are controlled by vacuum motors, either one has gotten disconnected, the vacuum line is bad or the motor is bad.