Fuel tank selector valve issue

I have a 1991 E-150. It has an auxiliary fuel tank and on a longer drive fuel started pouring out of the side of the van located more or less underneath the front tank filler neck. I was using the rear tank at the time and wasn't aware of the location of the fuel lines so I quickly switched to the other tank hoping it would stop the leaking. It did and I was able to drive it home. However, now that I've gotten under the van I see that fuel lines are nowhere near where the fuel was pouring from. My first assessment is that somehow the full front tank on that long drive I was on somehow pressurized enough and began to pour fuel out the filler neck (I do not know how). Although now I have been tinkering with it trying to find a leak. When I switch to the rear tank (the one I was using while fuel started pouring out), after about 20 miles an hour and some revs the engine chokes out as if fuel isn't being delivered. Switching tanks immediately solves the problem. And now no apparent fuel leaks are detectable. I'm quite puzzled as to what I should begin replacing. I'm not even sure if the fuel waterfall and the choking out of the engine are necessarily related, they just happened at nearly the same time. Also feel the need to note that while the fuel was pouring the van had no problems accelerating as normal, despite that with the rear tank, it does now.