I have a 2002 3500 Dually 4X4 with a 5 speed manual transmission. (106000 miles) Recently, in the last thousand miles or so, it began to be hard to shift between gears, up or down. It has gotten so bad now that I'm afraid to take the truck out for fear something will go out an I'll be stranded somewhere. It seems to shift better when it is cold but quickly becomes hard to shift after just a few miles of driving. I can shut the truck off at a traffic light and shift back into 2nd then restart the engine and be ready to roll when the light turns green but going to third, fourth and fifth is difficult. Any suggestions as to what is wrong???