Problem 1. I recently purchased a 1998 Ram 2500 4x4 Cummins. For some reason the transmission started jumping in and out of overdrive or constantly shifting when driving a steady speed of 40 -50 mph on flat ground. Other than that everything shifts smooth. Is there a sensor or something that could cause this?

Problem 2. After the truck is warm, the heat only sometimes blows good hot air. I've changed the thermostat and it's full of antifreeze. Any sugesstions on this problem.

Thanks For your Time,
Chris

 

Well how many miles does the truck have? becuase it may need a generaloverhual of the transmission which ismost likelya 518 or otherwords 727 with a overdive unit on the backend. Ummcheck the electrical sensor for OD checked and/or check connectioins for corrosion on either wires or inside ofthe plugs themselves.
Second your heater core could be slighty clogged and not letting mush coolant get through. Try a coolant flush and see if that fixes it.