You may be able to file a petition to establish paternity and have a Texas court order DNA testing to be done. There may be, however, some issues with jurisdiction and statute of limitations. In other words, a Texas court may not have the power to order and out of state resident to comply with its order. In addition, some suits have to be filed within certain time limitations.
Typically a bank or lien holder will not willingly remove a person from the note. The only way for your name to removed from the note is to refinance. However, it is unlikely that you can refinance without him or without him knowing.