The little screw thing on the top of the control box, if it's like mine, adjusts the tension on the throttle - this could explain why you are finding it quite stiff to operate.
The max rev range for the DF 70 is 5200 to 5800 revs, so if you are only getting 5000 revs, then maybe you are slightly overpropped.
As I mentioned in previous posts, my engine too is underrevving, but I am still *just* in the max rev range. I am thinking about reducing the prop pitch to 20" from the default 21" and also going to stainless..... in theory it should give me another 300revs approx. I guess it's a case of trial and error