Sold a used vehicle with incorrect Model Year listed on Bill of sale. Now buyer will sue unless I pay him.

     He can sue (anyone can sue for anything), but whether he would win depends on whether he can convince the Court either:      (a) that you misrepresented the truck to him as being a 2001 model, that he relied on that misrepresentation in deciding to buy the truck for the price he paid, that his reliance was reasonable, and that the misrepresentation was material (i.e. that the difference between a 2001 model and a 2000 model is something an ordinary buyer would consider when deciding whether to buy a truck); or      (b) that the two of you entered into the contract for you to sell the truck to him based on a mutual mistake, i.e. the mistaken belief that the truck was a 2001 model and not a 2000 model.