Jones Hold Up 03:42 9 Princess Stuntin' Like A. 
03:11 10 Dem Get-A-Way Boyz, Put On 05:04 11 S.L. Jones Ham 04:11 7 The Rich Kidz Bowling 04:06 8 S.L. Disc 1: 1 Intro 04:26 2 Yung Ralph, Oh Yeah Young 05:40 3, Big Kuntry King I'mma Fool Wit It 03:46 4 Pill Bunkin' 03:43 5 OJ Da Juiceman, In The Kitchen 04:07 6 Scrilla,, S.L. Jones Choosey Lady 04:59 12 Scar, Don't Do It Like Dat 04:08 13 Champ Squad Charge It 04:25 14 Travis Porter Freaky Girls 03:13 15 Trillville I Be Off Dat 03:58 16, Shawty Lo 2 Sides 03:30 Disc 2: 1 Da Bill Collector, Pill, S.L.
If you have your product's original packaging, you can check the barcode to find the serial number. 
If you have an iPhone, iPad, iPod touch, or iPod, you can get the serial number from the Devices tab in iTunes preferences.
3906 is the old one, parts not compatible with the first waterproof (3905) version or the newer yet 3903, the newer model #'s seem to be counting down. What happens when Traxxas gets to 1 the universe collapses I suppose! Parts that fit both old and new, Shocks, Wheels tires, depending on rim and hex size, Electronics, and that is about it. They beefed it up quite well with Revo parts when jumping to the 3905. If you have gray chassis, you have the newer gen. If it is black then older most likely.