hollowtech bb done 800 miles no problems, no play in crank arms at all,new chain fitted and its still the same, tried it with dif back wheel still the same
when i put a lot of pressure ie up hill or stand up and make a bit of a effort something is giving me gritty,noisy worn feedback through my feet and shoes its not the peddle bearings i tried that, its like you have a really gritty gunged up rear cassette and the chain is not gripping properly, but drivetrain is spotless and casettte is only 800 miles old as well
is this what shimano bb start to feel like when on there way out??

If you remove the cranks and turn the bearings by hand it should be pretty obvious if they're knackered.

bearings are probably fine. Sounds like there's sh1t behind the tophats though.