running rough

i have a 1999 2500 with the 5.7, 163.000 miles, today i noticed it was ideling rough and emitting black smoke upon excelleration from the right side bank.
my wife is the normal driver and she said it had been running fine., yes it has dual flomasters behind the cats and they have been there for a few years now, it feels like a old time carburator that is dumping to much fuel, so as of right now i am letting it cool so i can install new plugs, any other suggestions will be appreciated

Pull the trouble codes and see what the computer does not like.

Pulling the codes is the first thing, could be alot of things, o2 sensor, temp sensor, bad connection at either.
Many parts stores will pull the codes for free these days, and since yours is an obd II year it will need a code reader to get them.
Good luck