I have a 2007 dodge dakota with 170,000 miles. The trans was shifting fine as I was driving. Then all of a sudden it wouldnt shift. It stayed in 3rd gear. It wont down shift or up shift by itself. Fells like only 2nd ,3rd and reverse are working. To get home I would start in 2nd and then go to 3rd. Any thoughts what it could be before I go to the trans shop.Thanks for your help.