oh well in that case... all i can think of is buying a new stock... 870's are the most versitile shotguns ive ever used. there is every kind of stock imaginable for them. check out cabelas and bass pro. bass pro might have more of what your looking for they have a better turkey hunting selection

If thats the case why dont you just replace the thumbhole stock with a traditional one?
Either way though you will do just fine should you wish to shoot the 2.75" shells. I would stick with the #6's, and limit your shots to however far your pattern holds up. No need to change shot size or chokes.

get rid of the grip...

i like the idea of the 20g for you....also a semi-auto will take a good portion of the 'kick' out. one other idea is porting the barrel....you lose some whack but you also lose the kick in the shoulder.
if the pistol grip is the culprit I'd get rid of it too!

Standard stock with limb saver pad sounds like the way for you to go. Maybe try someone's gun to see if it is any better for you before you make the change.

If that is the case, you might have to sell the gun and get you a "normal" stock without the grip.

There are a few things you can try. It sounds like you are gripping the stock very tight. Less grip means less vibs. You might try a thumb hole stock by rotating your wrist more it may send less into your forearm. Also you might try an automatic they seem to shoot smoother. If you can afford it Benelli makes a gun with vib dampeners. I know how you feel I have lots of metal in me. And you can feel everything.

Limbsaver slipons are alot cheaper than most chokes and time spent on pattern tests. Good luck

I have three turkey guns and I added a Sims Limbsaver pad to all three. The pads are well worth their money, cuts recoil in half if not more.

If it's legal where you are, you might want to think about using a light rifle. I know that a lot of purist are going to slam me for saying that, but if you're injured and it's legal, who cares what others think. That's the option that I'm using this year, I recently had a very extensive back surgery, and my doctor won't clear me to shoot a shotgun, regardless of gauge, load size, recoil pad etc.. Where I hunt, a rifle gives me no advantage for distance, 40 yards is a long shot anyway, and besides I'm not into sniping a bird when the challenge is to call him in. It should actually be harder to hit a bird since I'll need to wait for a better clearing with a rifle over a shotgun.