I rode a 2006 TTR and really enjoyed it. I have a chance to buy one local now and it's a 1999. I'm in the US. Is there major model year differences between the 1999 and the 2006 in the USA?
Welcome to the forum!
A 1999 model is likely to be one of the last of the metal gas tank models. If it's an Open Enduro it will be mechanically the same as a 2000 onwards plastic tank "blue" model. If it is a Raid model (larger tank and different plastics) there are a few suspension differences - check out the FAQ page:
If it is the blue one then they are all the same and I think the US only got these models. The blue model started as a 2000 model year but I believe there some 99 builds AFAIK.