Are you running your SPI display at 5V or 3.3V? I bought this ST7920 module from buydisplay.com in China, but for 3.3V.
Datasheet timing specs may be different than your display module, depending on how it was built. I noticed from the ST7920 datasheet, that there is an external resistor across the controller's osc pins and it recommend different values for 5V and 3.3V. I think mine has a 27K ohm resistor (R7), while the datasheet recommends 33K for 5V and 18K ohm for 3.3V.