I had a big long write up for you that I thought I posted this morning but I guess I must have closed the browser before I sent it. I'll be way more brief this time. WHen I first read the thread, I immediately thought of IAC because I have had so many stick. However, they only affect idle and kick out as soon as you apply throttle. Next would be a major vacuum leak. It would be hard to find any vacuum leak if you have to constantly rev the motor to keep it running so you may look at the bigger vacuum hoses (like the pvc valve and brake booster hoses) to see if anything might have popped loose or dry rotted apart.

Being that the truck belongs to your friend, you don't want to throw alot of part or money at it so I would check everything that doesn't cost anything. I think you need to check your ignition system. It doesn't take very long to pop the distributor cap loose and check it and the rotor for corrosion. I would NOT take the ignition wires off more than one at a time so you don't mess up the firing order. Look over the wires for a burnt spark plug wire or frayed melted harness. And common issue with high mileage vehicles that sit around a lot is worn valve guides can drain oil into the cylinder causing the spark plugs to fowl out. I would check several spark plugs for good measure. Only a couple are pia to remove so pick a few easy ones and pull them to look at them. If you are running lean, they will be clean, if you are running really rich and not burning due to a bad coil or ignition problem, they may smell like gas. I don't think the 460 ever saw coil packs.

Next I would do the TPS check with a multimeter. It doesn't take very long. I personally don't think this is the problem, but its free to check if you already own a multimeter (VOM). As far as MAP sensors go, I don't think they can be checked without some special tools like an oscilloscope. If you lucky enough to have another vehicle with one or a friend with one, you might try swapping out to see if it makes any difference. Alot of Ford MAP sensors are interchangeable. If you are going to be close to Fort Smith, I have one you can barrow.