I just had my house rewired for a generator cutover panel that will be fed by a portable generator using a 50a power line. I bought a Firman generator from Costco rated at 8500w with a 50a receptacle. When we hooked it up today, every circuit that was running from the generator with lights on it had the lights (LED) flickering. I suspected noisy/dirty power from the generator so we turned it off and went back to line power. When I did some more research, I discovered that line power has a Total Harmonic Distortion (THD) of 5% or less. This Firman generator spec sheet said the THD was 25% at full load. I can’t live with constantly flickering lights while on generator power but probably even bigger is the concern i’d Have for my appliances and furnace running on such dirty power. Can anyone share positive experiences using a portable generator rated at 8k-9k watts with a 50a plug and low THD? Brand recommendations?