Join the club, Ihave the same problem with My AC. When I had the 200 amp panel, meterbase and service entrance put in, the poco didn't bother to change the drop off the pole, so I have 2awg drops feeding a 4/0 service entrance, in the summer time when the other 2 houses on the transformer are running their ac too, I get a very pronounced flicker.
This is the ac's third season, so far so good.

Trainwire