Car is back after receiving new fuel pump. All appears well. The car accelerates normally.
From my Invoice, the tech noted:
"installed fuel gauge into system to determine actual fuel pressures. Initial Prime and residual pressures are within specifications at this time. Test drove vehicle with gauge attached and found pressure is insufficient under load. Determined high pressure fuel pump to be faulty. [diagcode: D1350_00000000_02_002] Removed and replaced high pressure fuel pump."
So I recommend to all with HPFP failures that you ask your dealer to do this ["Test drove vehicle with gauge attached and found pressure is insufficient under load"], so you don't have to play charades like I did.
The part number for this pump is 13-51-7-613-933. This supersedes 13-51-7-594-943 which in turn superseded 13-51-7-592-881. My SA told me this new HPFP has only been out 2 weeks.
Also good information here by 1addict user "isitspringyet":
http://www.1addicts.com/forums/showthread.php?t=377318
I had a sneaky suspicion this has to do with ethanol in our fuels. The law here on the front range of Colorado stipulates it must be 10% for smog reduction. For those of you who use lower ethanol in your fuel, I believe you will have a lower chance of having a failure. But this is not proved yet.
Here's another link from wiki:
http://en.wikipedia.org/wiki/Ethanol_fuel