That did it. I found the following in the document:
Performance Counter Monitor- This monitor uses RPC, requiring the following ports:TCP/135; RPC/named pipes (NP) TCP 139, RPC/NP TCP
445, RPC/NP UDP 137, RPC/NP UDP 138
I created a custom GPO with those firewall inbound rules (TCP 135,139,445 and UDP 137,138). Actually, all it needed were the first 2 ports, and my server is now all green. Thanks!