As far as the clutch shoes go, the plastic one's will give you great grip, I would stick with those. I'm not sure about the integy one's, but the HPI clutch shoes are almost identical. The Savage clutch bells will fit your Volcano . You have the SH .18 right? I know it fits the SH engine, not sure about the VX engine. I run these clutch bells on my Tornado. I am using an HPI 18t Savage bell right now on it.
I can get another set of plastic redcat shoes, but for only a few dollars difference, would the aluminum perform differently? Yeah, I have an SH 18. How does an 18T bell work on the SH 18? Do you have the stock Volcano center tranny, or a different one? I have the direct-drive like in the Shockwave, and I think my 16T bell makes it geared a little high, so I'm thinking 12T or 13T will give some better low end good power.
You said it's just reving on an incline. Does it drive fine on flat ground? It could be a number of things. Besides the possibility of the clutch shoes, are your center dog bones slipping at the diffs? Check your grub screws. Do you have a stripped diff? Is it reving under any condition - stripped spur gear?
It drives ok on level, in grass/sand and other rough terrain it runs kinda slow, even though the engine sounds like its revving pretty well. On hard pack/concrete, the engine revs up pretty quick, but the truck accelerates slowly. The top end isn't what it used to be with a new motor and all stock gearing, but its still up there. Since it does go I assume the grub screws/drive cups are all fine and I know the spur is brand new. When I hold it in the air the tires get up to speed and balloon up pretty quick, so I assume its just a stupid clutch that is failing to transfer the power when its pulling against the weight of the truck.. Again, since it drives a little and seems to work when held in the air, I'm making the assumption that the diffs are still good too.
As for the engine, I have no idea. I'll try the glow plug and a retune from factory settings next weekend when I get some time, and see what happens.