I’ve just replaced the chain on the Anthem with a new SRAM pc991 running xt mechs and chain set all 9 speed stuff.
Was just gonna head out for a ride but only got to the first gradient (not even steep) when I noticed the chain isn’t running very smooth.
As it comes out under the middle chainring its like its still trying to stay in the ring and continue round rather than head towards the rear lower jockey if that makes sense?
It only seems to do it under stronger pedalling tension.

Would this be a worn chain ring? Or just maybe too many links left on the new chain? I measured the new chain against the old when fitting so it should be correct.
The Xt cranks are pretty old now M751 and have never had the rings replaced.

It sounds like your middle chainring is worn. Especially if it’s mainly happening under harder pedal forces.

If thats the case, it’s very likely that your cassette will be worn too.

New rings and cassette time!

New rings and cassette time!

Or else that new chain will become an old chain even faster.

As above, it’s new ring/s and cassette time.
Put your old chain back on till you get the new parts.