Towing.
 

I own a bbq catering buisness and sell bbq roadside. My smoker is on a trailer and its not that heavy just enough to pull the back end down a little bit. What can I do to keep it from pulling it down. I have a 3 inch lift on it.

How is your rear suspension currently set up? Full 3" leaf pack? Shackles? Blocks?
What kind of shocks are you running?

You could transfer some weight to behind the axle of the trailer to lessen the tongue weight if that is possible...

Not sure that the issue is with it lowering the back down, that's normal when you put a load on it. All you can do really is upgrade your springs.