Installed offroad h now lags?

No it won't hurt it. But it won't really do anything either. I would recommend reloading your tune, however. If anything would help, that will. But yeah, with 3.31's, you will notice a hit down low having an H pipe. But the sound is all worth it. If you're really worried about it, email Brent and tell him what's going on. Maybe he can tweak your tune.