It is a good idea to flush the system-, I also added a cooler when I did mine.
This is almost a kit (cooler, bolts, hose and clamps) Has almost everything you need to add the cooler. I used Summit 13222, 12 inch cooler. I mounted it to the tabs on the bumper- I had to buy 2 large washers and a hose connection to connect to the original return hose. I think I paid $22 for the cooler. It hangs behind the bumper, but is still in the air stream. Good cheap mod.
Chevy 04.5 LLY, 2X, shell, XDR, MikeL Heavy duty up-grade, 6spd, TransGo, deep pan, de-badged, 65 Gallon replacement Aero tank, LBZ-mp, Kennedy pump, shimmed, Pre-fuel filter, tow mirrors, BU cam, gauges, GPS, Sirius, bags, custom grille, fender vents, HD trans cooler- Curt front hitch, footwell lights, load lights, Studs, head gaskets.