Okay, somebody please calm me down so I can enjoy my day off. Le scoop: Been a working pro on some instrument since about '77. Exclusively a bassist since '91 or so, with a few intermittent semi-pro stretches. So when it comes to tone, hopefully I'm way beyond sightseeing. Anyhow... Got a GB Shuttle 6.0/12T combo shortly after they came out ('08-ish?), and have loved it. LOVED it. I've used it with all kinds of cabs for different venues/road dates, and have never failed to get a tone I really dug for any style on any of my basses (mostly Fender, J & P, flats and rounds). Recently bought a Fender Bassman 4/10 cab (neo), GREAT results in tandem with the 1x12 AND as a stand-alone. Best & most versatile rig (for me) I've ever had on any instrument. So, figuring I'll stick with this rig for a long, long time, I sent my trusty 6.0 to G.B. for cleanup, re-furbish... just check under the hood. G.B. service was everything they say; just great, responsive, etc. Very fortunate to get a loaner Streamliner 600 from my fave Nashville store (thanks, J.D.). G.B. called before the weekend (today's Sunday) to say the 6.0 was done & ready to ship. The tech said he'd "done all the stuff you listed, and did all the upgrades & everything." I didn't think anything of it, just said thanks. So, I HATE the Streamliner. I know some people love 'em. Did I mention that I'm not in that group? I've done about four rehearsals & three gigs with it, and regardless of what cab I use, what bass I play, or how I set it, the low end is just this woofy, wooly, undefined bowl of mush. Forget the nice Jamerson-esque thump of my P with flats. Bag the broader, chewy goodness of my J with rounds. I can turn down the bass pot, and pump a little of one of the mid bands, and get better definition, but all the meat of the low notes goes away. The 4x10 is pretty much unusable for me with this head. Did I mention that I don't like the Streamliner at all? I've read that the Shuttle 6.2 has "more extended bass." Okay, cool... unless what G.B. considers "extended bass" means the subsonic mush I'm getting with the Streamliner. I drove home from the tonal turd hunt that was last night's gig all panic-stricken; what if, when the tech said he'd "done all the upgrades," he meant that he 6.2'd my amp, and was sending back a nice, shiny bowl of mush? More fundamental on the low notes? I'm in. Bowl o' mush? Aaaauuugghhh! Nooooo! Please, somebody tell me that the 6.2 upgrades don't make the Shuttle anything like what I'm getting out of this Streamliner. Please. I'm one of those guys who can't focus on ANYTHING if I feel there's something not right in my setup. Yes, I've done a search. Yes, I've read umpteen threads, which ATE a perfectly good morning. Nothing that I can find really addresses it. I can't call G.B. on Sunday, obviously. My dogs want to go to the park. My honey-do list looks like a phone book. There's a T.V. show I really want to watch. Save me - get my brain outta this loop! BTW, I should mention here that I really don't care for the Streamliner, in case that was in doubt. Any input is welcome. I thank you, and my therapist thanks you.