DC 3 squeal/feedback issues

Hi everyone. I'm new to this fabulous forum. I checked every thread to find if anyone already left some lines about the resolution of my problem, but seems I'm the only one affected.
So... I'm impressed by the tone of this little amp, but unfortunately I can't deal with squeal/feedback problems that start when output volume is set on 2 while using the lead channel.
My guitar is loaded with a Di Marzio Crunch Lab in bridge position and a Liquifire on the neck.
I tried everything: potted the humbuckers, changed the tubes (with expert technicians) to find out if valves could be responsible for that, checked the board to see if there were bad soldered connections, checked guitar electronics to see if components failures were present... But everything seems to be just fine.
It's kinda odd: squeals are present only with my guitar, but not with others...

Can someone help me to find out a solution?

Thanks

Are the reverb cables connected correctly? I bought a broken DC-3 to repair and it acted this way because the reverb cables were reversed.

The correct orientation is shown on the tube chart in the manual.

It's probably not the problem in your case but it's worth a shot.

hi! thanks for passing by...
nope. reverb cables are not the problem: incredibly everything is just fine. I'm going quite mad about it...
Is it possible that is just a matter of power of my humbuckers!?

I had one dc3 and found that the batch of preamp tubes that I kept purchasing would go microphonic in that amp.
Had a set of burstbucker pro #2&#3 which were wax potted and they would feed back microphonicly . not a lot but enough. So I stopped using the EH higher gain 12ax7 . a set of ruby JJ cured it but didn't last long.

Only thing I didn't do was try mesa boogie.