My astrovan does that, too - unbaffled tank.

I would take out the tank pickup and do some measuring to see if it gets close enough to to the bottom of the tank. I've never dropped a 4cyl tank, but the v6 tank has the kind of baffling you describe on a swb v6, at least. May be too much pump for the application, or you have a leak in the lower end of the pickup tube that aerates when low.

Not responsible for advice not taken...