Your top plunger rod likely isn't centered, that would account for the bad seal and crazy friction.
I think that could be the problem, but am not sure of a solution for it. I have tried using a 1.5 inch fender washer with a 3/8 ID for my seal,which fixes my problem of the slow plunger rod; but it only gets a 40% seal and does not fire a dart. I have no access to large hardware store here in Hong Kong and my hardware stores do not carry fender washers, is there any other way of centring the plunger rod?