Here is my script, I don't see much wrong with it. Does anyone know why this might not be working?
game.Players.PlayerAdded:connect(function(player)
player.CharacterAdded:connect(function(character)
if game:GetService("GamePassService"):PlayerHasPass(player, 4583498) then
character:WaitForChild("Humanoid").WalkSpeed = 55
end
end)
end)
Makes 0 sense, should be working...

3 comments
I'll try this, thanks Sir. If it works I'll verify this answer.
It would be better to only connect this event if they have the game pass rather than checking each time.
I agree. Let me edit the response.