Help were at our wits END! 2000 Chevy Astro Van?

4.3 liter Vortec engine Starts Perfect! Idols like it is in an earthquake. Put it in gear to take off and that's fine , when you give her a little gas bogs way down like its gonna stall, then suddenly picks up and goes on. Check engine light is on and we had the code checked, Just says..random misfire. already changed Spark plugs, coil pack , wires,m air flow sensor, distributor cap, rotor on and NO luck PLEASE if you know help me.!!! asap.