American Motors: possible vapor lock????, fuel pressure gauge, 1978 jeep wagoneer

Question
Kevin
I have a 1978 Jeep Wagoneer.360,4bbl,auto with 150,000 miles . Motor has 20,000 since rebuild. Runs good and plenty of power.Problem is when I tow my tractor with the jeep(abt 6000 lbs),after 70 or 80 miles,it starts sputtering and acts like it wants to cut off, I decrease the accelerator pedal to about 25 or 30 mph and it runs fine. After it coold down,it runs great at all speeds and then does the same think. I have changed the fuel pump,all rubber hoses in the delivery and return lines,and it still happens. Please help as I am attached to this truck like it is my best friend and needs some help.
Thanks for any thing you can tell me
Bob

Answer
There are other items that can cause your condition.
Ignition coils often break down when hot & under a load, as well as spark plugs & wires.
You could hook up a fuel pressure gauge and check the pressure when hot while driving.
Is the temperature gauge indicating an overhating condition. What thermostat is in the engine?