Recently my 98 2500 automatic dodge has been having problems with shifting. when I'm driving about 45-55 mph it shifts up and down constantly. All the fluids are fine, but after i had changed the oil, it was working perfectly. I don't know why it does that and what the problem is. and its also at 309,000 miles everything stock. Don't know if i should replace the tranny or what the problem is. Can someone help??

 

Welcome to DF.

Check the throttle position sensor. If the RPM change is right about 200 RPM, that is a good indicator the sensor is going bad.

 

Welcome to DF! Also check out the 2nd gen Ram section. Lots of good info on transmissions and other common problems with these trucks can be found there.