AudiWorld Forums - 99 1.8t turbo surge/stall??

I have noticed recently that between %75-WOT (according to vag-com my throttle only opens %86-87 at WOT) the car cuts in and out. For example today I was going up a moderate incline at 60-65mph in tiptronic 5th gear. When the boost pressure guage indicated around 10psi it cut back to 1-2psi and then back up. It did this about 6-8 times then I looked down and it indicated 15boost when it stopped (I have had it to 17psi and normally it just cuts in and out or it will kick down a gear). I have a stock airbox that has been modified by smoothing out the interior and cutting out the bottom with a panel k&n, 3"test pipe to a 3" exhaust, aftermarket turbo inlet, front mounted intercooler, and speed tuning stage II chip. I have gotten the following off vag com in the past two days on two occasions:
17963 - Charge Pressure
P1555 - 35-00 - Maximum Limit Exceeded
17544 - Fuel Trim: Bank 1 (Add)
P1136 - 35-00 - System too Lean
17658 - Fuel Level too Low
P1250 - 35-00 -
Readiness: 0000 0000
16806 - Main Catalyst; Bank 1
P0422 - 35-00 - Efficiency Below Threshold
I do have the stock and I am assuming original diverter valve. Anyone with any ideas and or what to look for on vag-com would be greatly appreciated. This is my first go around with forced induction (2 x MKIV VR6's , 16v MKII, 78 diesel rabbit, and a ration of aircooled) and all of these extra hoses make my head spin. Thank you in advance.