Got my BD manifold in yesterday (man what a pain with the dual shocks). I used new gaskets on the manifold and the collector and she fired up with no evident problems (visually or accoustically). But I seem to be smeeling a bit more diesel exhaust in the cab every so often. Am I paranoid, could there be a leak, or is it just that the provided firewall grommet doesn't totally seal? Anything suggestion on what I could use to seal better it? Thanks.

Likely paranoid. You can get someone to plug the exhaust while you check for leaks. Either that or you can look in a few weeks and you will see soot where there is leaks. I reused my gaskets and had no leaks so with new ones you should be fine as long as you tightened everything down.