390's are finiky when it comes to oil weights and even brands. I've had 'em that rattled like a coffee can full of rocks with anything but Esso oil, 30 wt. And they ran for years on it. The original lifters need a LOT of oil to them to work right, aftermarket ones are better.
Did you change weights or brands when you did the pump job? And you might want to change the filter brand as well.