Don't make any rash decisions wait a day or two.
I totally understand where you are at. 2 years ago I was in the exactl same spot as you. And I was going to sell my car also. But what you should do it hold out for a better price than what your going to get on a trade in.
Driving that tiberon your going to be frustrated as hell and end up blowing out the gears powershifting like me
The way I look at it I see a few options...
Pull all the mods off your car and trade it in. Or atleast the heads and intake. I know those aren't helping the trade in value whatsoever and you could definatly sell them. (I'll buy that holley intake)
Keep the car, look for a used honda or acura or something like that in the 6000-7000 range. Puts your payments at only 150bux a month for 5 years and gives you a nice daily driver.
Or trade in the stang, or sell it, get a newer daily driver, and pick up a cheaper fox body and slap on the parts you pulled off your GT.
I understand the frustration, it really sucks.
Skyler