I've had a Ruger Redhawk 8" 44mag for about 10 years. I can't hit shit with it! Seriously, it doesn't group at all. I would think an 8" barrel you could hit things far out, I can't hit a paper plate at 20'.
I try adjusting the sights and I'm chasing the "groups" all over the place. I'll get a couple shots here, then there.
I'm thinking about taking it out one more time and trying it off a solid rest before I send it back.

I sent an SP back once. I swore It grouped high and right. They sent it back with a target with a nice group right at bullseye, the revolver shot from machine rest. There may be something wrong with your gun, but I'd get someone else to shoot it before you send it back.

Could be a bad gun, could be you can't shoot.  Be honest with yourself.  Have at least a couple guys try it, ones used to shooting handguns with recoil.

I honestly don't think it's me. I can shoot playing cards with a S&W 642. I put hogue grips on it to help hold the beast, but it's just crazy.
I know what the one guy is saying about thinking his gun shot off to one side, at my range the sun comes in from the left I'll think all my guns shoot left, the glare on the side of the sight screws me up, but if I concentrate I can still shoot straight (with other guns)

If you shoot at an established range, ask if they have a Ranson rest and the correct grip insert for your gun, you might be able to use it for a nominal fee.

Did I mention that I was so confident that my SP was screwed up that I paid shipping, not Ruger? (Gun is older.) I swore up and down it was the gun. I even shot it from rest and still I got the same results. I shoot handguns quite a bit, which probably made me overconfident about my ability. Never wholly trust your own judgement.

Otherwise, how does the crown look?

As above, before sending it in, I'd get some FACTORY ammo of a different type then you're using and have another shooter try it.  Don't use the same ammo you've been using.
This positively eliminates any possible ammo issues.
Don't tell him anything more than that you can't get it to group.  If you tell him "It's shooting high and left" that may influence the way he shoots it.

If he can't get it to shoot.... back to Ruger.

This is not uncommon.  
You can get a Ruger that will shoot as well as any gun you've ever seen, and another made at the same time that just won't shoot.
Invariably, after a trip back to Ruger, the gun shoots well.  It's strongly suspected this is all barrel or barrel installation related and Ruger corrects the problem.
I've seen any number of cases like this with Ruger firearms.