[s-cars] 00519 code G71 sensor signal too low (kinda longish, PITA to me:( ) boost issues

[forrest bradshaw]

a month ago I had hit overboost at 30psi and fuel cut which then cut my boost back to 15psi, I also found code 00519 had been stored.  took car off the road for inspection, found a crack in my Stromung downpipe where it bolts to the turbo and also 5 EM leaks due to loose nuts.  So I had the downpipe rewelded (very nice too) and installed a new RS2 EM and reset the ecu.  checked the wastegate and it functions properly, blew into the nipple and sucked through it and it held pressure so I believe the diaphragm is not leaking (don't have a vac tester).  I also replaced the WGFV thinking that caused the 30psi overboost.  when I pulled the turbo I noticed the exhaust side of the turbine was kinda white as was the EM and the entrance to the DP.  I associated this with the 00519 code and car having been overboosting.  

I've been very light footed for almost a month now even after replacements and last night I went WOT, at first there was some stumble and then after two pulls it smoothed out and was fast, wow I like it again.  and then it started to stumble again under boost, thought is was going to stall, felt like the MAf died but I just replaced it with new last fall from FAP99.  got home and scanned ECU, got the 00519 code again saying G71 signal too low.  since replacing parts peak boost returned to its normal 24/25psi then settles and stays at 20psi.

Now I am here at a complete loss, dont know where to turn or what to do, Forgie said to check the plugs, that I am doing this evening after work as I will also clean the MAF connection.  

judging by the code I think its cutting fuel and not misfiring, though the exhaust does sound differant, sounds like very lightly audible miss, sounds like a old muscle car at idle, but more refined like a URS sounds if that made any sense?

in 1st gear am also getting 1 pronounced big stumble which nearly stalls the car.
mods are:
MTM 1+ from Pastore and 3bar VMap
Stromung gen II turbo back and catless

replaced WGFV with known working unit and EM

new MAF last fall (old one was on fritz)

1 code  00519 G71 signal too low

car is sad, makes me sad

thanks for any help guys, and Dave thank you too!

Forrest