Fast Flight,
I've found the Gamemasters vary quite a bit from bow to bow. Here are some things to try:
1. Make sure the brace height is correct of course. The GM,s that I've shot don't do well with low brace heights. 8"+ is better. The stock strings are really ropes too. Get someone to make a quality string for you.
2. A set of limbsaver ultra solids mounted on the belly of the limbs at the fadeouts will help control the vibration from the limbs
3. Lining the limb pads on the riser with cork or some similar material will help. Be sure to keep it thin (around 1/16"), and replace the limb bolts with 1/4" longer ones
4. A stabilizer or riser weight screwed into the stab hole will help vibration and will improve the balance of the bow.
5. If you have a shaker, my guess is the limbs are a big contributor. Replacing the limbs with a quality set will do wonders for that bow. Most short ILF limbs can be adapted to that riser. Any of the older short Hoyt Gold Medalist limbs make an excellent upgrade, and can be found used for pretty reasonable prices. The Gold Medalist carbon plus foam core limbs are an excellent choice. The older carbon plus maple cores are also excellent limbs.
Start with the easy / cheap stuff and see how it goes. The Gamemasters can be made to shoot really well. Some are pretty good right out of the box. Some need a little help. If you don't feel like hunting stuff up yourself, I have most all the parts on my website to do the work. I'm a sponsor here so I'm easy to find.
Hope that helps ........... David