In all honesty as you’ve tried a lot of things already I’d book it in with a decent tuner, tell them what you’ve looked at and I’m sure they’ll get to the problem pretty quick.

You already have a new loom which is excellent news and expensive so no point really selling your old management (which sounds in good condition ) just to fix a misfire which could be something cheap and simple...

No need to entertain a 4K management swap at this stage imo,
The rich with money to burn may think it’s an option though...

Hope you get it sorted, keep us posted

Cheers Paul