If fuses, power lines and grounds are all clean and tight then good cahnce its the switch. Suspect same relay is used for stalk and headlight switch? A 4 pole is only $30. If switch is wired without a relay on both low and high beams 4, the feeble contact points in the switch do not last long from arcing. If you know terminal wiring on switch you could bypass the switch contacts to prove its the switch. Probably easier to buy a quality new switch and swap it out. Ensure there are relays in the circuit.
$35 from Speedway motors-
http://static.speedwaymotors.com/pdf/91080154.pdf