Had a problem develop with the Verada KS this afternoon - started to miss badly

When you rev it in park - no load - it will rev cleanly to 3000 rpm and then start to miss. It revs up then revs drop and it tries to rev again when you hold the throttle open. Doesn't matter what throttle position it won't climb above 3000rpm. Same symptoms with air cleaner element removed

Plugs are 15,000 old and distributor cap was replaced at the same time

Any ideas?

Thanks

You will need to check the basics.
Plenty of fuel?
Spark plugs - pull and compare the six. Dark plugs are the ones misfiring. Oil on the plug body?
Plug leads - measure resistance with a multimeter. Oil on the leads?
MAF plug - clean?
Engine error codes?
Compression test.

Revving the cr#p out of it won't help.