I think Champ is still playing at a very high level.
A couple things to keep in mind:
1. He's getting challenged more these days because the other DBs are holding up their end. In the past, there was no reason to throw his way when guys were constantly open on the other side.
2. With all due respect to Miller, Doom, etc., one of the reasons Denver is leading in sacks is because of solid coverage in the secondary.