GSM 3G Power problem - Device keep refreshing

Dear all,

Please refer to the attachment. I'm trying to design a 3G modem running on windows 8. Due to PCB design error, there is problem with the power output. The recommended input power is in the range of 3.6v - 4.2v.
The power is supplied through LTC3113 and is configured to receive 3.3v as input, and to supply 4v to the module.
After making the necessary rework, i've got the result as attached (Channel 1=input, Channel 2 = supply for the module)
Modem detection and operator searching work fine when plugged in to the PC, however, when it tries to get the signal strength info, device manager keeps refreshing and makes sound of device detection continuously. After a period of time, it times out.
I've checked with an oscilloscope to see if there is a sudden voltage drop due to pulsed load, however there is no such occurrence. (simulation with LTSpice also suggest the power supply should be able to handle the pulsed load with minimum voltage during this period at 3.6v)
I believe this to be due to the power supply design since the module operate well with 3.3v supplied by TPS51225. However this voltage is not within the recommended range.

Best regards,
Faizal

Anyone has any insight on this? I've tested this on two IC. Prolonged usage in this condition caused the booster to fail.