SD card and GPS shield problem

Hey all,

Here am facing problem with the GSM/GPS Shield, i ordered few months ago a GSM/GPS shield (rev.6) and it stopped working for unknown reason, and due to time limit i didn't send it back for checking so i ordered another one, and i got to know that the one i ordered now is (rev.8). and there is some changes in it from the previous one.

the problem is when i connect the two modules separately (GSM/GPS shield and SD shield), they work perfectly, but when i connect them together the SD card stops working.

i connected GSM/GPS shield to pin (53)
and connected the SS pin for SD to pin 22
MISO, MSIO, SCK are common between them

P.S. i already had few tests before with my SD shield with GSM/GPS shield (rev.6), and it was working perfectly.
i also tried to use another arduino mega board...but it have th e same problem

Can you please tell me what exactly should i have to do to make both of them work perfectly (SD and GSM module rev.8). any advices or suggestion will be appreciated...