AFAIK 55*C is perfectly fine for a chipset as long as it doesn't go much higher than that. I know you just built up your rig, so is this what has been registering since you got it working or has it just recently begun to startup at that level? Also, keep in mind that motherboard sensors are fairly notoriously wrong, so as long as you notice no instability or anything, should be just fine. AFAIK, 55*C is normal for an Ultra-D's chipset and just about everyone's chipset for that matter as most stock heatsinks are pretty darn bad. If you're really concerned, you could start by replacing the stock TIM with Arctic Ceramique, and if still concerned could always just replace it. Should really be perfectly fine though <shrugs>