Soggy brakes even after bleeding

Hi
Has anyone got any advice on bleeding brakes on a jimny?
I've never had any problems before bleeding brakes on any car i have had, even when I first fitted the rear brake conversion on the jimny. I have just replaced the rear passenger side caliper and now I can't get the brake pedal to harden up.
It feels fine without the engine running, but once the engine is started the pedal drops and its a soft pedal
I have bled the brakes over and over but can't get them any better.

Any advice, before I revert to a drastic last resort and take it to the garage?

Have you bled the rear brake balance valve first, that has a bleed nipple on it.

Yes bled the balance valve

I put the rear wheels up on ramps then the fronts when bleeding. Air rises so this I figure this helps with helping the air along.

Have you bled in the right order, I.e. starting furthest away from the master cylinder and working your way in?

Possibly a seized caliper?

Clamp off all the hoses and remove one clamp at a time when bleading unless thay are braided ones