cat. converter???

Alright, I posted about a month ago about my 1995 Toyota 4Runner having problems. The rpms would go up but I would go the same speed. I had several people tell me it was the transmission. Well, I had the transmission fluid changed and that seemed to work. Now, about 3 weeks later, it is doing it again. I couldn't get above 40 mph while trying to get on the interstate. My dad says that it maybe the cat. converter. If it was the transmission I would think it would do it all the time. It only does it sometimes and then stops for a while. Is it possilbe for the cat. converter to be stopped or plugged up for a time, then break loose later and give me my power back? Also, I can smell a kind of sulfer smell coming from my car. If there is anything else it might be just tell me please. Thanks for any help.

Could easily be a clogged cat conv.
Symptoms I've had for a clogged conv:

Cherokee - loss of power climbing hills, had to shift to 3rd where 5th would do it before.

4Runner - loss of power period once engine got hot, let it cool down and power came back.