Shifting Problem
 

I have a 1999 Dodge Cummings 5.9 with 210,000 miles on it. All of a sudden it has its own mind as when to down shift.
1. If I am going 60 miles per hour and need to pass a car when I put the pedal on the floor it usually does not down shift, and takes forever to build up any speed.. Sometimes it does not downshift at all, other times after I have about completed my pass all of a sudden it kicks into passing gear.
2. Driving 40 - 50 miles per hour, steady pedal it might down shift in and out several times for no reason. Any information will be appreciated. Thank you.

ADDED INFORMATION
 

It seems two be two different problems. I fixed problem #2. It was a loose ground cable. I still have problem #1. Even at 50 miles per hour. Pedal to the floor it won't shift into passing gear. Any help will be appreciated. Thanks

sounds like your kick down cable is out of adjustment.
this happen to me on my truck went to a tranny shop fixed in 10 min.

The trans shifting in and out of OD is AC noise issues. You need to test it as it is slowly destroying the ECM, VP, PCM and other electronics in the vehicle. You will need a new alternator. It will need to be tested as well when you put it on.

https://mopar1973man.com/topic/9004-...nt-alternator/