2004 Ford Ranger Stalling out

My ford ranger has recently stalled out several on several ocasions. I took it to Sears the first time the replaced my battery saying that it was leaking. Two days later it stalled out again. After a little while it started back up and I drove it another mile or two before it stalled out again. From there I towed it somewhere. I started it back up again once I got there, it ran for a while til I reved the engine a few times and it stalle dout again. It wouldn't restart after that. I took it to a shop and the mechanic said it's runnin fine he can't get it to miss a beat nor stall out. I thought it was the fuel pump, I'm lost to what it could be though.