i have a 2003 dodge 4wd quad cab cummins
scenario: i get in my truck go about 40 miles down the road pull into a parking space (truck is warmed up and hot now). now i am backing out of parking place i put it in reverse back up and then put it in drive to continue driving down the road. it will not shift and the rpm's go up really high. if i force it it may shift but most of the time it will not. if i can get it to shift by forcing it when i go to put on the brake and slow my truck down it will do a lagging and jerking thing. most of the time i have to stop my truck put it in park and then put it in drive in order for it to work properly. this happens in the summer time sooner than it does in the winter.

does anyone know what is causing this and how to have it fixed?

thanks,