Yes, check the "T" fitting under the S/C snout. They like to rot there. And of course all other vac lines. Sounds like it's time for plugs/wires/fuel filter and then go from there. Take a look at the "Safely modding your 3800" thread to get the proper brand and type of spark plugs. No Platinums or Bosch. Go w/ lifetime warranty wires. Delco's are good.

Are you running at least 91 octane fuel in it? If not, then do so before you destroy a piston or 2.