Paultx:
RCBS dies, in my experience, are fine, never has a problem with them, in any caliber. I would suggest that you adjust the FULL LENGTH sizing die exactly as per RCBS instructions.
As I mentioned, not setting the shoulder back to far will definately help with case life. There used to be a couple of gages available, with which one could check how far the shoulder was being moved back. Mo DeFina used to sell one of them. Don't know if he is still in business though, haven't seen/heard of him in years.
I assume you are using a single stage press. Bring the ram to the top of it's stroke. Screw the sizing down until you have firm contact with the shell holder. Back the die out about 1/4 -1/2 turn. Resize a fired case. Check to see if the bolt will close on this resized case, likely it won't. Screw the die in a little, say 1/8 turn at a time, and try the above step again. Do this till the locking lugs go home (the bolt closes) on the test case.
At this point, you will have set the shoulder back quite close to the minimum required for proper function. Now turn the sizing die in the smallest increment you can, check the test case again. If the bolt still closes fully, the locking lugs are flat, lock your die where it is. Do tis with a case in the die, as everything will then be centered. By the way, when checking for chambering, as above described, operate the bolt by hand, with operating rod and spring, the extractor and ejector removed. Doing this is not really a big deal. Having a vise is a great help in reassembling the bolt, unless you are one of those lucky people who have three or four hands.
One other thing you might pay attention to is "wire drawing" of fired cases. Reloading and firing such brass can lead to head spearations, leaving you with a broken case, stuck in the chamber. If you happen to have a broken case extractor close at hand, not a large problem, othertwise you are stuck, with a disabled rifle. Check for wire drawing as follows. Straighten out a paper clip. Bend a small "L" shape hook at one end. Run your tool, "L" bend forward, till you bottom on the inside of the case. Move your tool till the "hook" is against the inside of the cartridge case, still bottomed on the case head. SLOWLY drag your tool out of the case, keeping the the hook against the inside wall. If you feel as if your hook "falls into a ditch, then climbs out", you have found "wire drawing", and that particular case is likely on it's last legs, and should not be fired, lest you experience head separation. The procedure sounds a lot more complicated than it is, and it will work with fired cases in any rifle, though wire drawing is usually less of a problem with bolt guns, due to reduced tendency toward case stretching.
If you are already familiar with the above methods, nothing lost. If you weren't, then the above might save you some trouble.
Enjoy your Garand.