If you have put 800lbs of weight on the implement and it is not doing the job, then you really need to look at what you are doing and what it is that you are doing it with.
I know that this is late, but the problem with putting down pressure with the 3pt is that all you are doing is picking up the back of the tractor, thus loosing traction and or putting much more stress on the front drive axle. So like was already said, you need either a big and or heavy tractor before the down pressure thing really works without causing other bad side effects.
As far as your rear blade not cutting, for these to work well you really need to have about 100lbs per foot width or more and have the cutting edge set at the proper angle. Most of these blades simply do not weigh enough, so to be able to make full use of them, very common to have to wait for the ground to be damp to be able to get much work done.
Just sort of how it is.
Good luck.