David Stanley Chevrolet mislead me Oklahoma City Oklahoma

We purchased a 2009 Chevrolet Silverado from David Stanley in Oklahoma City on 2-27-09. I traded in my 2006 Dodge Ram which I was upside down by almost 11k. They told me that if I did not like the truck I could bring it back in 72 hours or 300 miles, whichever hit first. I made this purchase on a Friday and tried to take it back to them on Monday. They told me that because I drove off the lot that I owned the truck and they would not take it back. They then showed me where I signed stating that I could Exchange this, but they do not have anything else they could put me in. They listed my down payment as cash and keep calling me wanting a post dated check for the down payment. If I don't give them their $3000 by 5:00 today they are going to start legal proceedings. I don't understand this, that they gave me 30 days to pay. (it has only been 10 days). My signed contract list my down payment as cash. In addition I bought the Tires for Life - stupid on my part. Their tires for life program won't even cover my vehichle because I have oversized tires. You would think they would know what is covered on their own programs.

David stanley chevrolet is dishonest
oklahoma city, Oklahoma
U.S.A.