The first thing you need to do is check the little handle under the seat on the right side. If it is in the up position you are in draft control and it'll act like what you've described if you have a weak ram. Another thing the 8N is famous for is the pressure relief valve on the pump. Pull the right side cover on the rear end housing and reach down under the pto shaft and find the thing sticking out of the back of the pump that looks like a spark plug. Once you are sure where it is start the tractor and put your finger over the end. If you feel any fluid flow it's bad, it's about $18 bucks or so at your NH dealer. While the cover is off you can cycle the hydraulics and use a mirror to see how much fluid is coming out of the lift piston. If these things check out OK you need to hook a pressure gauge to the test port at the right front of the pump housing. Chain the lift down and try to raise the tph, you should see, if I remember correctly, 1900 psi. You could also have a gasket blown out on the pump or lift cover but you ought to be able to see that with the side cover off. It's a pretty simple system.
