Are you saying that the valves turn harder since you rebuilt them, or did they always do it, or do you not know because you never used the manifold before rebuilding it? If it worked fine before, you did something...who knows what. Here's a wild guess that is probably useless, but if there was silicone and now there's PTFE grease, (Christolube) it's possible that the PTFE grease is light enough so that it doesn't hold up under the big pressure differential. I would NOT bet on that as an answer, though. You can try making sure you have the thickest of the PTFE greases and using a bit more on the threads of the seat carrier. If it always did it or you don't know, you're probably just finding out the machining limits of your manifold. I suspect that manifolds with very well machined threads and better tolerances do work more smoothly, but I don't know what brands those are or even if there's a big difference.
I had a problem with my iso valve being difficult to turn, not after rebuilding the valve, just after removing and re-installing the manifold for the tank inspection. The iso bar turned freely in the threads, it wasn't binding, yet somehow the valve itself was much harder to turn, tank empty or full. I never figured it out, I just assembled the doubles again, and it mostly went away. This is with a blue steel manifold, not one of the best. I've never had any problems with the post valves themselves.
Look on the bright side; sticky valves will have a harder time getting rolled shut in a restriction, and believe me if you ever have a big leak while cave or technical diving you'll have enough adrenaline to turn anything.
