Fitted a new chain, cassette and jockey wheels to the Deore XT on my Cube Reaction Race. Since doing so, under pretty heavy load (steep slopes), I'm getting "chain suck" with the chain locking itself. I've only had this once before in the terrible mud of the Strathpuffer. Given it only does it under load, I'm not really sure what I'm looking for - the only thing I can think is that the RD isn't providing enough tension. Hints and tips would be greatly appreciated!
ROAD < Scott Foil HMX Di2, Volagi Liscio Di2, Jamis Renegade Elite Di2, Cube Reaction Race > ROUGH