What is the sag on the shock? If you very gently sit on the bike while someone holds it, how far does the shock compress? It should be only 20-30% of its full travel. Could you have too much air in the shock? I know I tend to use less air than the charts recommend depending on the bike.
If you're going to have it re-tuned, call Push Industries and have the stable platform valving, ProPedal, installed. It is soooo worth it.
http://www.pushindustries.com/servic...20Air%20Shocks