Mine were very stiff as well for the first couple of times. I agree that you should check the torque on the socket bolts. This snip is directly from the owners manual available on the Equal-i-zer web site.
Never tow with loose socket bolts. Tighten socket bolts to a minimum of
45 Ft-lbs torque before each towing session.
CAUTION Do not pound directly on the sockets to move them. Pounding may cause
the sockets to crack or chip. Use only the lever force of the spring arm to
move tight sockets. Loosen the socket bolt if required. Re-tighten them
once the socket has been moved.
Insert spring arms into the sockets in the hitch head. Arms for the 12K
and 14K models are side specific. They are notched slightly off-center, and
should be inserted into the socket with the notch on the inside, and with the
label facing outward."
With all this said, I would agree that a little grease on the socket surface should allow better movement, but you may want to consider loosening the sockets and then re-torquing them.