Gigabyte P45-UD3R + F2-8500CL5D

[gerdp]

I have 4 sticks of F2-8500CL5D (2x 2GB + 2x 1GB) for a total of 6GB.
I was using the 4 sticks in a GA-P35-DS3P board with E8500 C2D- absolutely no problems.
Upgraded to GA=P45-UD3R rev. 1.1 and running into problems with the same E8500 and the 4 RAM sticks.
If I put any two of the sticks in any two of the mb RAM slots of the UD3R - everything works fine.
However, as soon as I add a third stick, the board does not POST. Get a sequence of short beeps, indicating RAM problems. Same result for 4 sticks.
Tried all combinations of 2GB & 1GB RAM sticks and mb slots, same result.
Using F11 BIOS with optimized settings under MIT.
Is this a RAM or mb issue?

[Tradesman]

I'd start with the 2GB sticks in 1-3, the 1GB sticks in 2 and 4, enter the base timings and DRAM voltage manually also set command rate at 2T. tRFC needs to be at 68 or a little higher.

[gerdp]

Tried the parameters you suggested (2GB in 1&3, 1GB in 2&4, base timing 5-5-5-15, increased voltage to 2.0 (from 1.8),command rate 2T, tRFC to 70) - same result as before - board is not POSTing with short beeps.
What else can I do?

[Tradesman]

If all the sticks run fine in the other mobo, you may have an issue with the mobo, have you tried raising the NB Voltage, maybe up it .1 or so?