If your US license(s) are still valid, DLT will issue you car and motorcycle licenses good for 2 years. Get a medical certificate (100-200฿) , copies of passport ID page, last extension stamp and a certificate of residence from Thai Imm. It takes 1-2 hours only. At renewal with the same documentation you'll get 5 year licenses. I think the DLT will charge you 750 ฿ for both licenses when issued and renewed.