The fact that the bolt is hard to open after firing makes me suspect the chamber is contributing to the problem you are experiencing.
When the round is fired, the case will expand in the chamber. If there is crud on the chamber walls, it can stick and be very difficult to open.
Take the rifle apart and clean the chamber with the proper brush until it shines! Likely yours has varnish deposits from not being properly cleaned after shooting steel cased ammunition.
Disassemble the gas valve and clean the port in the barrel, all valve parts, and reassemble. Inspect the piston and gas tube and insure they are clean and move freely. This would be a good time to check the fit between the outside of the piston and inside of the tube wall. A large gap here will keep the rifle from cycling properly. If the parts bind, the rifle will also have problems cycling.
To reinstall the operating rod, it is easier if you use a punch to push the operating rod and compress the spring with one hand while closing the retainer with the other. It needs to be fairly stiff, but should move freely in the housing without the spring installed. This is another area where clearance is important, but a large gap could create problems.
In most cases, proper cleaning and lubrication is all that is needed to make an SKS run reliably.
The Yugos sometimes have issues with the gas valve, which is adjustable and can become blocked.