Won't Start

[aklytzky]

I went driving to the store all seemed fine. I turned of the car did a little shopping. Then when I returned car would not start. I changed out the module amplifier and it started back up again. idle would vary from high to low but once I got going felt fine. I also noticed that when I would put it in reverse the car would stall out. so after two days the truck just would not start anymore. It cranks as if it wants to start but does not turn over. I replaced battery, cap & rotor, spark plugs and wires, and even the coil. any suggestions?

[o2batsea]

engine/year please