What tells the truck to put out more amps under stress Computer?

 

I have been unable to determine if the ECM controls the output of the alternator, but if everything checks out OK, there are wires coming from the Batt to the alt, heavy gauge, and a wire coming to the alt field to provide current for the alt to start charging. Check if you are getting voltage to the alt with that wire. What you can try is this.
Unplug that wire coming to the alt.
Connect a wire from the positive term of the battery through a light bulb,#194, to that terminal on the alt. if you have your voltmeter connected to the battery at this time you should see the voltage reading go up.
Let me know what you find . Thanks ,,,,hanky

 

Mark, This is what I'll bet you are overlooking.
Part of the positive cable from the battery comes across the front of the truck and goes to a junction on the back of the driver's side fender well just behind the power steering reservoir. Lift up the plastic protective cover and You will probably see come heavy corrosion at the cable terminal and the other piece that has two fusible links that feed the inside of the vehicle. This would be your high resistance connection on the positive side. You will need to disconnect the battery before taking it apart , but then you can do the job right. Let me know if this solves your problem, it should! hanky

 

cant belive it a power wire to the altenator was loose and not getting power to the altenator all the time it went on and off at will ran a new power wire and it fixed the problem thanks for all the help hanky i found it by taking your advice with following the wire to the box