Sounds like you need to run straight pipes for a while, and have lots of early morning starts/long warm ups.

 

with the loss of power etc.. sounds like a crossfire/backfire kinda deal. make sure the plug wires cross at close to perpendicular and maybe try some higher grade fuel or octane booster to see if that makes a difference. could be carbon causing predetination.

 

You are describing exactly as the above poster stated. To me, it is without question your catalytic converter is going up. Starts with a rattle like popcorn or marbles bouncing around. The worse it gets you develop power loss. Then you will notie horrible gas miliage untl one day you hit the pedal, the trannie revs, and you don't move. I hope you fixed your problem.