02 gmc Yukon xl 5.3 whole lot of nonsense

127xxx, runs great. Just got it 3 weeks ago. Took it straight to oriellys and ran codes, co265,po171 po300, po420,po442,po446,po174. I replaced power steering pump and pulley. I got and cheap scanner and hooked it up now it says p1518. I disconnected ground on bottom of block on srivers side so I could move wires,did just not reconnect it good? And what happened to the rest of the codes?I think something is wrong cause the engine sounds funny, sorry but it just sounds like it's running rough?idk. Any and all help will be greatly appreciated

reconnect the ground and replace the intake manifold gaskets. clear codes and drive it around the block. then check the codes.