I would replace your thermostat and gasket while you're doing a coolant flush, very cheap items. What I like to do, remove my thermostat and take off the old gasket and place it back in the housing and bolt back down. This way I can flush the system without fulling warming the system, goes a lot quicker. However many flushes of distilled water it takes to run clean. Then install the new stuff & bleed. Heck your could even replace your Tensioner while you're messing with the coolant and elbows as mentioned above. Although most people don't, they should be replaced with your belt. Advance Auto sells the Litens brand, which is the OE for the GP.
I would also recommend using the Goodyear Gatorback belt, which was renamed/bought and is now the Continental Quiet belt. I get mine on ebay for cheap. The catalog is on continental-elite.com. My stock '08 GP NA 3.8L is P#4060905 for the belt.
