I have a 1994 Chevy Silverado 1500 4WD with a 5.7 eng. And a 5 speed trans. It starts and idles fine and runs fine under throttle out on the highway. The problem is just off idle, like in first gear pulling out a driveway with very little throttle or out on the highway at cruising speed in high gear with very little throttle it cuts out and bucks and acts like it is loading up like running with the choke on or something. I have replaced the plugs & wires and the dist. Cap & rotor. Any idea what would cause this?