fluctuating rpm

[iron rick]

I have a 2001 Montana I recently purchased 85000 km I have recently been noticing on higher speeds 80-100 km (45-65 miles) the rpm has been jumping and when this happens you can feel the van jerking almost like it wants to bogg out. It doesn't do it all the time but has been getting more frequent. Any and all ideas as what might be the problem would be great.

[sharo23]

seen catalyst converter cause simalar problem