cybed, two issues I can see after a quick look:
1) lack of depth. 4 LBs and 6DBs leave you open to teams wearing you down in the 2nd half.
2) defensive sets. You are running the nickel against the I for sure, and getting pummled on the ground that way. To make matters worse, you are wearing out your DB's that much faster, so when your opponent DOES pass, he's doing it vs. tired DB's.
Feel free to sitemail me with further questions.