Question: My new Canon EF 75-300mm telephoto lens and the zoom ring is quite stiff. Is the lens faulty or is there a way to loosen it up?

Answer: 
I had similar sounding problem with an ef 75-300 I bought about a year ago,
It felt almost as if the outer casing of the barrel was rubbing or catching in places against the inner making the movement feel a bit jerky!  

over time however using the zoom ring seems to have become a more fluent action, 
the front focusing ring is soft and smooth but it always was so,
I suggest if the lens is still covered by warranty that you contact your supplier and discuss your concerns!
regards
M
I recently had the same problem, as the lens was stiff and felt like it was scratching. I took it back to the store where it was purchased (Currys) and they immediately sent it off to Canon to be repaired. Apparently it is an easy fix, but I didn't want to try myself in case it invalidated my warranty or screwed up the lens.