If you had it running well before I would lean toward a cleaning issue.
I'd take the gas piston out, clean it, clean the gas cylinder, clean the inside of the gas plug too. Clean the gas shut off screw oriface. Leave all them bone dry on the inside. If you lubed it you might be gumming up the lube with powder forming a dirty paste. If you greased the interior parts for storage like I do, you must remember to clean them of the oil and grease before the next range trip. Excess bore solvent can also migrate into the gas system via the shut off screw. One is often cautioned to clean the guns upside down in a cradle to keep the solvent in the bore.
You might also take a look at your ejector spring. Tear the bolt down and look at the spring, are there still gaps showing between the coils? I like to compare old ones springs with a new unused one, I was especially doing that with Garands as they were all over the map in wear from CMP.
That's all I got if your op rod is rubbing on the stock.