Engine Mechanical problem
1995 GMC Jimmy 6 cyl Four Wheel Drive Automatic 147000 miles

While driving down the road. Get to around 50mph the car begins to buck and shake rpm fluctuates transmission feels that it slips. Stopped and sat for a min and began driving but the power was gone. Acted as if was not getting throttle input and would not go over 30 mph on flat ground. The fuel injectors and fuel pump and filter have been changed recently. It also will not go into 4wd and a slight whining comes from trans what would cause the complete power drain? Checked the map sensor and throttle position sensor both good