Personally, with 75 lbs of live rock in a 54g, I'd just ditch the cannister for a while and see if that helps. You mentioned earlier that you're not sure how much it helps you with your biological filtration anyway. And looking at your stock list, you don't really have a huge bioload. Just make sure you have enough circulation once you remove that source of flow.
I agree that if it was the Eheim, then the casing should be warm. But then again, if it's the culprit then it has found its equilibrium with your tank water and should be more or less the same temp as your tank.
The heat has to come from somewhere. If you haven't had the heaters plugged in, or the UV
plugged in, then it's either coming from your Eheim, your powerheads, or your skimmer. I'm assuming your skimmer is working fine, so it's probably not that. Are all your Maxijet's working? Occassionaly, in my salt water mix tub, a MaxiJet will get crudded up and stall. I know it happens because I can't hear the hum anymore, AND the water temp is about 2 degrees higher than normal. I can't imagine that's your problem because you're talking a 20+ degree difference. That's a lot of Watts and the biggest power consumer I see in your tank right now is that Eheim.