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Cruise control problem

I have a Chrysler 1999 Town and Country Mini-van with 124,000 miles. The problem I have is my cruise control works when the car is on level road. Any time I go uphill, the speed starts reducing gradually and the transmission does not downshift to keep speed. The car gradually looses speed until I hit 45 MPH, and then the transmission downshifts to the next lower gear, and will keep speed around here (45 MPH) and not downshift to any lower gear until the uphill is gone, and then gain speed gradually till I reach the set speed. However, when I am approaching this uphill, or when on the hill, if I jab on the accelerator, the transmission downshifts right away to lower gear keeping set speed or thereabout depending on the % slope, so helping the car this way I can keep the speed but not the actual set speed. On the other hand, going downhill on steep slope, the transmission will downshift gears all the way to maintain set speed. I have tried other discussion groups - saw one other person with similar problem but no one has figured it out yet. Thanks

I don’t know what system the 1999 Chrysler had but it does sound like some cars that had vacuum problems.

Weak vacuum to the servo (check for cracked vacuum lines or loose vacuum fittings) or a leaking servo.

Thanks for the reference to the Servo. Actually, it ended up being the Vacuum tank that serves the servo that was leaking. There was a TSB on this vacuum tank dating to August 1999. Bought new Vacuum tank with new vacuum lines and now the cruise works perfectly and I am not loosing even one mile below set speed.