van sluggish

Van barely has any power. i can get it up to about 30 mph if im lucky. Sounds like is is misfiring but not sure if that is the culprit. I recently changed out my plugs and wires. Not sure if my coil pack is bad or my catalytic convertors are clogged and whether there is a way to tell which one or need to change both? Or could all 4 of my cats and my coil packs be bad all together? it is a 2000 econoline e150 4.2l 6 cyl. 229,970 miles. any help or suggestions would be much appreciated.

Ok. found out I had clogged catalytic convertors and my coil pack was bad. Now I think I have one more problem. Van will idle all day long good in P or N but if I switch to R or D it wants to stall out. Any suggestions on what needs fixed??