I've got a similar problem with my Cossie managed RS Turbo.

I've replaced nearly everything on the ignition side of things as it starts misfiring when it's warm (fine when the engine's cold).

It gets worse when I try and hit boost as well. The next thing I'm about to try is wiring up a independent earthing wire for the ignition amplifier. Apparently they benefit from having their own shorter one direct to the car's chassis.

Will let yo know if it works or not as I'm doing that over this weekend!

Cheers,

Andy