My 80 mi rides were before I got covid and long covid last year; now mostly 30 mi and less, plus weights, walking, woodturning, and other escapes. My MGUS is asymptomatic, and my kappa/lambda are now fairly high (damn), but other things can influence energy levels. A big one is grieving and the associated stress, sleeplessness, and not knowing what will be slapping you around next. Give yourself some time to grieve; most people with MGUS will not get MM, but the possibility is hard. It is good that you are proactive in addressing the MGUS. Elevated kappa/lambda levels can also be caused or at least increased by other things, such as inflammation (in my case celiac and colitis), kidney disease (check your kidney bloodwork), and who knows what else. Symptoms of fatigue, joint pain, or other can also be tied to other factors.