“Hardware is fine” and “with no load” do not fit into one sentence. You must STRESS that CPU and RAM. Last time I used Stress Prime 2004 Orthos. But that Router was a x86 PC and I was able to boot Win32 to run that test. Under MT ROS you should run a bandwidth test with UDP to stress NICs as well since they generate heat and need a lot of amperage to run in a typical big router.
With some Intel x86 dual-core systems I have found BIOSes to need flashing for updating.
Don’t forget to post what you have tried as well as the results.