S6 "sputtering" puzzle

[DGraber460 at aol.com]

My 95 URS6 has been demonstrating some strange behavior that I cannot  
diagnose.
Back in December my Inter-cooler sprung a leak. It was relatively easy to  
find the problem with a pressure test and I replaced it thinking I had cured its 
 ills.
About then we started to accumulate snow that finally stopped  somewhere 
between 70-80 inches total. The roads were so packed and rough that we  broke the 
oil pan on our A6 dropping on all the unavoidable holes  etc.
Anyway, now that the roads are passable I find the car  still "sputters" at 
WOT and full boost. It doesn't buck or cut out it just  sputters. If I peddle 
it to maintain below 17 it pulls like a train. Go to  WOT and 20 or above PSI 
and she sputters badly. Prior to all this it was  running 27 full boost very 
nicely.
I have pressure checked it twice with a stethoscope very methodically  and it 
holds pressure even after I take the regulator off. It also  blinks no codes.
Any usual culprits for such misbehavior?
Any advice greatly appreciated.
TIA  
 
Dennis
Denver
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