Is the FSB speed 133MHz? On some gigabyte boards, even if the BIOS says "133" an on-board jumper also needs to be "shorted" to 133. Get the manual and look over all the jumpers and what they do, find the one that changes the bus from 100 to 133 and check to make sure you set it to 133. Because 13x100FSB = 1.3GHz which is a 1500+ and 13x133FSB = 1.73GHz which is what your CPU should be.
A) Check the jumpers
B) Make sure the BIOS is also set 133
"Opinions are like assholes, everyone has one"