This weekend my 04 3500 Cummins did something odd. It didn't want to shift into second. It would wind out and remain in first for a long time and when it shifted into second it would shift hard. After that it would shift normally unless I came to a stop then it would do it again. Fearing I might have low tranny oil I stopped and checked the oil per the owners manual and it was fine. When I got back on the road everything was working normally, it shifted out of first like it should and all the way up into OD.

This has done this to me once before, but only briefly and during cold weather so I dismissed it, but it seems like it's something I'll have to address. Any idea why it may be doing this?

Cheers
-Bob

 

Try Fluid and filter change

 

I did a fluid and filter change less than 10,000 miles ago. The problem started after that. It did it once or twice briefly a few miles after the change and seems to becoming more frequent.

-Bob

 

Sounds like maybe to filter is not seated correctly. IE sucking air.