So, this is where I'm at now. I did a little research on the issue and one thing I read said to jumper the FX loop and see if it comes to normal volume. I jumpered it and it did indeed come up to volume. Still seems to be lacking that punch in gain though.

Now, what is the suggestion?

EDITED:

As I'd previously pointed out it appears to be pedalboard related. So, I did a bit of troubleshooting and removed a rack mounted GEQ from the loop and BAM! It's working again.

I'm not convinced that's the only issue considering that when the FX loop is completely unplugged there's very little sound from the gain section.

On a side note I switched out the phase inverter tube just to see if that could be the problem. Nope.