Check your code first. The PCM wants to tell you something.

A bad cat can do what you describe. The honeycombs on the inside physically break into chunks and when they turn sideways, gases don't go through them to well. My old VW Jetta did this and it bucked like a bronco for about 20 seconds, slowed down to a crawl, I put it in nuetral and blew out the motor, then it was fine. Good thing too as I was in the middle of a 3 mi long bridge with no emergency parking lane.

But there are other things that can do this, conceivably a MAF meter, IAC valve, bad coil - who knows? Go to this web page for a list of codes. If it is the cat, a O2 code might occur since you sensor is just upstream of the cat.

http://fordfuelinjection.com/?p=1