After I uppgraded the BIOS the mtrr looks like below, and now it works if I boot with mem=4736M so I can use all memory but it still doesn't work without the mem parameter then it will run as slow as before.
reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1
reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1
reg02: base=0xc0000000 (3072MB), size= 256MB: write-back, count=1
reg03: base=0xcf800000 (3320MB), size= 8MB: uncachable, count=1
reg04: base=0xcf700000 (3319MB), size= 1MB: uncachable, count=1
reg05: base=0x100000000 (4096MB), size= 512MB: write-back, count=1
reg06: base=0x120000000 (4608MB), size= 128MB: write-back, count=1