listen to what these guys are telling you! Take the 2500 and either put on on your loan or buy this!
http://www.on3performance.com/mustanggt.html
If your dead set on getting that vette, or any other car. Do not take 3500 for yours! The dealer I work for will give you more than that and you wouldnt have to buy anything from us!
OR
put your car on CL for 6k OBO someone offers you 5k and you are $1500 ahead than if you just trade it in for the vette.
you have a lot better options than finding that lender who will just turn you upside down.