1997 Dodge Ram Erratic shifting

I have a Dodge Ram truck that is shifting erratically. It has done this for about two months. Last week the truck seemed to loss power and would not regain power. At the start of the problem I could regain power at about 2,000 rpm and proceed but it has got alot worse. My mechanic serviced the transmission and stated that the filter was clogged. I have power now but I still have the erratic shifting
In his opinion he thinks that it could be related to the catalytic convertor. What do you think could be the problem?
Thanks