Your truck came standard with RWAL. 4-wheel ABS was an option. Which system do you have? Post a pic of your inner fender if you don't know which system you have.

That said, the symptoms you described is spot on for a faulty speed sensor located in the top of the rear differential. It's about $20 at your local parts store and probably in stock.

If you wanted to pull the codes first to 'troubleshoot' the problem, the dealer has the scan tool to access the abs codes. The scanners used at parts stores can only read emissions codes. But the dealer will want $100 just to plug in the scan tool.