Provided the head is matched to the mass and COG of the camera/ lens system, any upgrade to it will do little to solve the shakes problem.
It most usually isn't the head that's the problem, but the support underneath it.
It sounds like yours is seriously under - rated for the task it's being asked to perform.
With those lenses of yours you really need the tripod equivalent of a 2 tonne block of concrete.
The only ones I KNOW for sure can perform such a task are these, tho' undoubtedly there are others out there.
http://www.bhphotovideo.com/c/produc..._Fibertec.html
If you can afford them (and the mid level spreader + bag etc) don't hang about, they've been discontinued since Christmas, and once B&H sell out, that's it.
My review of same:
http://www.dvinfo.net/articles/camsupport/fibertec1.php
I'm afraid you won't get the level of rigidity required with anything costing significantly less.
CS