I use a cheap, no-name grinder a friend picked up for me on Amazon, and it works great for the Firewood. That said, the material you're using could also have a lot to do with your problems. If you're not getting a fine enough grind, try turning the grinder over so you can re-grind everything. You definitely shouldn't be winding up with pea-sized chunks! (Which is how big I assume they must be if you're having trouble getting it down the chamber.)
I haven't found gumming up of the chamber to be an issue for me, even when I do neglect to clear the load while it's hot. So far I've been able to very gently brush out the chamber with the flat end of a wooden skewer, and it's staying surprisingly clean. I've actually been surprised by that (of course, my last small portable was a Pax, so anything less than super high-maintenance totally delights me).
My herb isn't very moist or sticky, for the most part. Maybe that's the difference?