At the top of any TDR page, got to the Discussion Forum drop-down list and scroll down and click on User Control Panel.
On the user control panel page, go to Edit Signature on the left side menu and fill in the details about your truck. There IS a 250 character limit on the details, so if you have alot of mods, be sure to put the important ones first, obviously including the year and model of your truck.
Also, on the user control panel page. you can edit your Truck Profile to include as many details as you want, but those will not be displayed at the end of every post, only under your truck profile when people go to look at it.