mine are really nice still but the housing insides are better thoughYou should put that second new bulb on the other side. Bulbs dim with age, and you will probably now notice one side is brighter than the other. Also, use some of that bulb socket grease they sell in the little packets at the parts store. I think it's actually just dielectric grease. Lubs the base and helps keep it from any kind of corrosion.
My taillight sockets were a bit brownish also, caused by heat and age. The whole harness plugs in under the bumper in the corners on each side and can be replaced, don't know how much they are though.
2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18
metal heat shields at the sockets