Note: ALL engines burn some oil @ high RPM's. I would guess the valve seats are carboned up/worn. When you repalced the head gasket was the head inspected by some one? If not that was your 1st mistake.
Honestly IMO, NO additive does what it's makers claim it to do. If these products are so good they would be in your engine from the factory. I've heard good claims about Engine Restore(sp?) but once the damage has been done NO chemical will fix it. Kinda like a manual trans grinding & the person drains the 10w-30 engine oil for a heavier 75w-90 gear lube, little do they know they're making problems worse then they already are.