I have a 2001 5.9 cummins just purchased with 140,000 miles just noticed after a few thousand miles of driving the tranny has been acting up shifts great 1st-3rd going into 4th and over drive it revs up high and doesn't wanna shift if I'm rolling at about 40 mph then if I let off gas it shifts or I give it more fuel same from 4th to overdrive any recommendations? Fluid an filter was also just changed in trans

 

gov pressure transducer most likely, but check all of your battery terminals and round connections.