I'll be completely up front with you.
As a co-signer, you are liable for his debt. Meaning that if he makes late payments on the truck, they will report to your credit file, if it gets repossessed, the bank can come after you to recover the debt.. The only way to remove your name off the loan, would be if he was willing to refinance the truck in his own name or sell it.
RE: Child support
Take him to court and get your money.
RE: Your Credit
Read this http://www.creditfirm.net/blogs/5-simple-credit-repair-tips.html