yikes, 5153 Red with TS in front? :shock
I've had a similar problem with SD Blackouts, none of the hi-gain amps seemed tight enough in the low-end. I've swapped them for passive pups and hi-gain amps became easier to dial-in.
but anyway, try what everyone else suggested, try different IRs, because YES IT'S A BIG DEAL.
also, not every hi-gain amp plays nice with tubescreamers in front, certainly not the 5150 II (6505+ in real life I think), or the RED channel on a 5150III.
also, .74 for drop G on a 27" is too tight for my taste, both sonically and in terms of playability, but perhaps that's more about personal preference.