Mk III - R2 tone mod - ?

I have a 1990 era MKIII long chassis head.I run it thru a V-30 Bogner open-back Shiva 2x12.

Is there a mod that can add some more highs to the channel (remove or change a resistor or cap)? I guess I'm wondering if anyone else thinks R2's kinda dark-sounding.

I've never found my Mark III blue stripe to be dark sounding.

V30's are bright sounding and should sound even brighter in an open-back cab, so there may be something going on with your amp.

Worn power tubes can roll-off the hi-end.

You may want to try some preamp tube swapping - try changing V1 and the preamp tube(s) associated with R2 to brigher sounding tubes like an EI Gold or similar. Stay away from JJ's which I've found to be dark sounding.