I have a 2002 3500 Ram Cummins Diesel that will not shift out of 1st gear until the engine redlines on the tach, then it shifts into 2nd gear with a bump and goes through the rest of the gears fine. After 2 days of this problem, I reset it by disconnecting the batteries and it ran better for a little while, but now it will not go into overdrive and still has the low gear problem. I only have 46,000 miles on this truck. Any suggestions?

 

your transmission is going into a "limp" mode. the factory sends them into this to get you home when there is a problem with the trans. Undoing the battery resets the computer till it finds the problem again. You will need to go to a dealer or a good transmission shop (if there is one) to get it scanned and fixed.
Good luck.