[Spurshot]

If you get convinced you have filled it completely and still have an issue, add sticky thermostat to the list.

Bad water pump is low on the list. Water pumps show in worn bearings and leaky seals, but still keep pumping water.

You just flushed the radiator, so it's not likely a problem.

You mentioned the fans came on, so doesn't seem likely to be an issue either.

Not the overheating problem, but just me, 6-7 year old car, I might change all the hoses, thermostat, and maybe water pump pre-emptively depending on mileage. For a high mileage engine, belts and idlers & tension pulleys too, while you're under the hood. Nobody seems to remember the idlers and tensioners. They have sealed bearings and wear out like anything else. One of my past trucks had an LS engine that made 225,000 with me and the idlers were worn out by 135,000 miles.