I found this customer service response from G-Skill:
We see many customers have problem to run on GA-EP45-UD3P motherboard. some customers even found out that using 1:1 is not working but 5:4 is fine. looks like it is motherboard memory controller ratio problem. please try 5:4, which change FSB to 1333 and memory stay on 1066
I do not know what this means. Is this a BIOS operation?
Yes, you change the RAM/FSB ratio in the BIOS. What speed is the RAM currently showing up as in the BIOS? You need to manually set that RAM to DDR2 1066 speed with 5-5-5-15 timings at 2.1v according to the manufacturers specs. If you have everything on auto in the BIOS, the RAM is most likely running under clocked. The motherboard owners manual should tell you how to adjust the RAM speed/timings/voltage. You may have to press "Ctrl + F1" when you get into the BIOS to unlock some of the settings.