I would agree with dropping the sugar from your poultry rub...try a rub with lemon zest or some other means of adding a citrus flavor. Poultry seems to get alot of enhanced flavor from acidic/tart additives, as it is such a mild meat. I also like to use oil or butter to tack the rub to a bird when I shake it on...this also helps give a nice golden brown at lower chamber temps.
As for beef and pork, if you get carried away with sugar it may eventually burn as well. Use less to start with, then add more if you want a darker/harder bark. A blend of about 15% total sugar by volume should be a good place to start your rub mixture.
On most of the roasts and pork ribs I've done lately, if I want added sugar, I put in on after the first half of the smoke for a lighter and somewhat softer bark...this will allow somewhat deeper smoke penetration, as the bark will form slower without the sugar.
Good smokes!
Eric