What do I need to do to my van

I have a 1990 Ram 250 5.2 fuel injected dodge van, 125,000 at least. I had a friend put a fuel pump & filter on it in 12/06. In 9/07, I noticed whenever I parked on any kind of incline the van wud not start. No matter which end was facing up. On level ground it wud start first time. However when the shift passed thru R on the way to D the van wud stall. I have to start from N. There it’s no problem. Also my gas gauge stays on E it never moves. Also if I try to completely fill the tank I notice some leakage from the tank. The gauge never worked after the install of the fuel pump. My friend had to rip some wires on account of an alarm system he couldn’t work around. The leakage and the incline problems started about 6 mths later. The van runs great when its running. Have at it and thanks.........

Bill
p.S. I tried to make a donate but the system wud not accept my address. I wil continue to try.