transmission shifting

Have a 2001 3500 turbo diesel dulley and the problem is it shifts in and out of over drive when driving at a steady speed at 48 mph. It also occurs at 34mph and shifts back and forth from 3rd to 2nd etc. If the vehicle is under acceleration at these miles per hr. It does not occur passing the 50mph on the speedometer. Have been to the dealer so far twice .First they said it was the break light switch that was causing the problem. The truck was ok for a few weeks and then started again. Bringing it back again they needed to contact chrysler as to what elese it could be. They were told a bad Ground connection was to be looked for. Battery cables I noticed were cleaned an what elese I dont know, but paid the 100.00 dollar deductable. First time for the switch was 235.00 dollars, not covered under the extended warrenty. As of today a month later it started again. Called custemer service and explained the entire episode, which I am glad they will refund my money, but my point as I explained is, I just want this problem resolved. Checking this forum out is anyone aware or heard of this problem and a solution to correct this issue?

P.S. Prior to my having this problem, I did meet an owner with the same problem and approached me if my truck had this issue. Well found out that Chrysler coulden't correct it, so I now see him driving a Ford Dully, and I really do like my truck. THANKS

output speed sensor? its on the trans cheap and easy to fix

Will mention it on 1/17th when I bring it in again to the service manager.
Also Chrysler refunded my 235.00 dollars as a good start.
Wed.1/6 added 2/3 Qut. atf+ thinking it may be short, why?
Because the atf dip stick does not fit flush onto the tube because the bottom of the dip stick seems to hit the bottom of the pan from day one.Doing so the condition stopped and drove for hrs. to make it reoccur again to no avail. next two days nothing till sat.when flooring the vehicle to pass,caused it to come back.
Thanks for your response,
hope they try it.

I'd think that you may have found where the tranny wants to shift; I've had several auto trans vehicles that did that at a certain mph, and they ran for years w/o problems. For the O/D to 3rd shift, just don't put it into o/w until you're over 50.