I have strong letdown and H was fussy during day feeds too, although would take lovely relaxed feeds at night.
As well as feeding more often (3 hrly), I'd also try feeding him when drowsy (e.g. immediately on WU from nap, still swaddled if you're swaddling and still in dark room if possible - I know this is tricky with a toddler around though) and perhaps try feeding in a reclined position to help him deal with fast flow.
Maybe have a look at this too:
Oversupply and Overactive (Forceful) Let-DownAs H got older though she was/is better able to deal with the fast flow and so it's not such an issue any more.