"Chain Suck"?

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
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There is no secret ingredient - Kung Fu Panda
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There is no secret ingredient - Kung Fu Panda
London Calling on Facebook
Parktools
Blimey - apart from the Puffer, I've hardly used the granny ring. The bike's main duty has been as a Highland winter commuter, shod with Ice Spiker Pros. In fact, the granny ring got used so infrequently, the FD often wouldn't do the shift if required to.
But, reading the blurb, it does make sense. I'll take a closer look at the tooth wear tomorrow.
God, no. you can pick up a granny ring for about £5 normally. CRC regularly have some clearance offers...
I'm just thinking that the other rings will be dead too. That granny ring has done nothing compared to the other two.
Will the Deore rings fit the Deore XT - I guess so? I'll be needing another cassette, BB and chain in time
There is no secret ingredient - Kung Fu Panda
London Calling on Facebook
Parktools