Gas leaker.

1998 Mazda B4000 4x4 truck, 152,000 miles--in good shape. Question--I've noticed that when the truck is parked on a steep incline (rear of truck much higher than the front), with a full gas tank, gas leaks out and covers the front half of the bottom of the fuel tank, and it is wet up both sides of the tank as far as I can see. It is not coming from the filler cap--looks to be coming from the TOP of the tank somewhere (towards the front, near the center). I wouldn't think this is normal, but really don't know. The fuel pump was replaced about 3000 miles ago by a dealer, so am wondering if maybe something wasn't installed correctly, or is loose? Or possibly at this type of angle maybe this is normal with a completely full gas tank? Replies are appreciated. I asked this question in the ford ranger section since this truck is basically the same thing, but had no responses and figured I'd ask it here (even though I don't see B4000 listed, and this IS a truck, not a car). Butif anyone sees this question and would like to replythank you.