Welcome to the site. I would start by changing all the fluids. I don't know how much of a grease monkey you are, but there's no shame in going to Jiffy Lube to have them change out fluids. Just don't let them sucker you into buying anything else!

 

When I got my '02 their was a significant amount of the dexcool sludge in the radiator and reservoir, where the stick is. It took almost a year for the sludge in the reservoir to break up after a full flush and coolant replacement. If you're going to do it yourself, just remember that if you flush it with water from a garden hose (which is what I did) make sure that you don't get the engine too hot while you're running in cold water, and know where the bleeder screw(s) are on your engine to let coolant into the top part of the engine when you refill with coolant-my V6 has one, I think the V8's have two (this is very important!), but this may be different for your year, I don't know for sure. Get one of the Haynes manuals or something similar like Everett said and you should find the procedure in there if you want to attempt it yourself. Also, make sure you aren't mixing the Orange antifreeze (dexcool) and the green stuff, it's my understanding that mixing them creates a precipitate which can clog up your cooling system. My V6 has the green coolant in it now, so I have to change it more frequently, but I've got another vehicle that uses Dex and they've both worked fine so far. If you look around on the net you'll find people arguing the merits and demerits of Dexcool.
Even after rinsing out the reservoir it didn't really get super clean during the 1st flush. It's slowly become more clean as the coolant has been cycled in and out. I think Gorn is right on the money, when I first saw that sludge I was concerned it might be oil related myself, but haven't seen any sign that it was since the flush and refill.