My truck hesitates and sputters while driving?

I have a 1996 ford f250 4x4 with a 5.8l 351w engine. It runs strong until it is put under load such as going up a hill. If I floor the pedal it will run strong under load no problem but if im just lightly pressing the gas pedal it will sputter and hesitate like crazy, it feels like its misfiring and skipping. It seems to do it especially when the overdrive has kicked in and the rpms are lower. But even if I turn the overdrive off you can still feel the skipping but nowhere near as bad when the O/D is on. The truck also stalled on me a few times in the past two months. I would be coming to a stop sign and as I was coasting to the sign it would just stall and not start right back up, it would just crank but not fire. I would have to wait 5 to 10 minutes then it would fire right up. It is really ticking me off because I changed a bunch of things that I heard could cause these problems. Here is what I have changed: fuel filter, throttle position sensor, idle air control valve, throttle body, distributor cap and rotor, air filter, used fuel rail, new gas tanks (front and rear). I have been dealing with this for months and its driving me insane lol. Please help if you have had this problem and resolved it or if you have any input.