In search of suggestions.

No I didn't Gary. 10 shots with JSB 8.44's yielded an ave of 618 with an sd of 3 fps. I tried cleaning out the lock-up mechanism,various barrel tension settings,cleaned barrel with brass brush/JB paste/Ballistol...ect. Increased/decreased trigger weight,re-retightend stock screws,3 different scopes,iron sights,piston seal,breech seal,reinstalled stock spring/guide,did the tissue test.Tested with 9 different pellets. I'm just taking a break from it. Next, I'll try Holy water,bath water,toilet water. If nothing else works, I'm afraid that it's going to be wrapped around the maple tree in the front yard. !#@% ...sorry,Thanks for asking.
 
That’s a bummer Mike, one last thing have you tried shooting with the front of the stock resting on a bag. It’s looks like your have done everything thing else or there’s something very wrong with your barrel. Are you sure the wife hasn’t been at it?

Dont destroy it just yet maybe someone like a pro tuner will be able to get her shooting again. Good luck 

Gary
 
Seems like you've covered it, but I had multiple springers that built up residue in the breech over thousands of shots. One in particular shot quite well, then literally 1 shot to the next, went to hell. I went through a similar process to yours and ultimately sold that very good rifle. Found out later what it was and that's now one of my first checks. It took fairly serious scrubbing in the breech for it to be truly clean. 

Bob