What are my legal rights to get my Jeep back & give it to my 16 year-old son for Christmas?

I own a 1997 Jeep Grand Cherokee that was in need of repairs and planned to give it to my son for his 16th birthday. Last Christmas 2007, my son told both me and my ex-husband (his father) the only thing he wanted for Christmas from both of us was to get the Jeep fixed and ready to drive when he turned 16 in August, 2008. My ex-husband arranged to have the Jeep towed from my residence and taken to a mechanic friend for the repairs. After 3 months, I received a phone call from the guy who had the Jeep, explaining that he had tried all he knew to do, but was unable to trace the problem and needed to be sent to the dealership for further troubleshooting/repair work. After several attempts of asking my ex about his intentions, he has repeatedly assured me over the months that he will take care of getting it fixed. Finally, a few weeks ago, I decided to call the mechanic myself to find out the cost of repairs and make arragements to get it back home, but his phone number is no longer in service and my husband will not return my phone calls. To date, I still don't have the Jeep in my possession, nor do I know where it is located to go get it.
Can this be considered a "stolen" vehicle? It is paid in full and I have the original title, which is solely in my name.
Do I have any other legal rights that can be pursued to take further action against him and/or to get the Jeep back in my possession?