Help on mpc5200b and 1:1 CPU:bus clock ratio

Hello, this is our custom board's u-boot:

U-Boot 2009.08 (Apr 19 2010 - 05:35:19)                               

CPU:   MPC5200B v2.2, Core v1.4 at 132 MHz
       Bus 132 MHz, IPB 132 MHz, PCI 66 MHz
Board: Ran Controller Board
I2C:   85 kHz, ready
DRAM:  128 MB
FLASH: 64 MB

We have 1:1 CPU:bus clock ratio and for now we are having problems with Fec drivers (I suppose). 
Using 2.6.33 kernel, during a ping session, we have 60% packet loss.
We can't change kernel.

Where could I find the problem in the kernel? 

Thank you so much

Lorenzo