Brunning...odds are it isnt the grease. When you adjust the bearings there should some 'play' or 'looseness' to the adjustment. If there is no play before you clamp them down then you can bet they'll be over tightened when you clamp the quick releases. When the quick release is clamped down the cones and locknuts get compressed. This compression takes up the intial 'looseness' that was intentionaly adjusted in. A test you can do to see if your adjustment is to tight is to flip your bike upside down. Rotate your wheel so the valve stem is at the '11' or '1' O'clock postion. The weight of the valve stem should should cause the wheel to rotate with the valve moving to the bottom. If it doesnt, your adjustment is to tight.
I adjust my hubs based on the amount of play when they are clamped into the frame/fork. I loosen them untill there's play then tighten them down a fraction. Needless to say my wheels spin forever.