I had an unusual occurrence on a three leg trip today. First leg, 140nm, all was normal. 169kts TAS cruise on 14gph at 5500; full MP, 2400 rpm. This is very normal. I usually see 169-170kts TAS at cruise with varying fuel burn based on altitude. Second leg, 150nm, 5500feet same settings but only 160kts TAS. Third leg, 190nm, same settings at 8500 feet. Here is the strange part, I was only cruising around 155kts TAS. Then it would drop down as low as 147kts TAS and go up to max of 163kts TAS. It bounced between those min/max speeds about 3 or 4 times. Engine was running smooth, no fluctuations on CHT or EGT, RPM or MP. I have talked with my close RV friends and we are thinking maybe clogged injectors or air induction leak. Any thoughts or ideas out there? Similar things happened to you? Would love some feedback.