I changed my PMD to heatsink. Couldn't pull old PMD out to pull resister out.. I run fine for a while.. Then idled high after 20 or so starts.. Pulled old PMD off I.P and fitted resister after some mods.. Idled perfect..
Only issue is now it cuts out like key has been turned off.. Suspect key switch issues.. ??
Seems to stop when going over pumps..

Check your wiring. The harnesses on these old trucks seem to be getting a little worse for wear. I've been changing out the engine harness as I work on vehicles.

Also change the harness that the PMD extension plugs into or that plugs directly into the PMD

In my case it's a 05 Workhorse P30 built as Winebago in Australia. Has 70,000 klrs on it .,

Be leary of MAde in China harnesses and parts.

Any good heat sink will work - much handier to have them already drilled and tapped though.

I'm not sure what is available there. I think both SS diesel and Leroydiesel.com will ship to you.

About all I like from SSdiesel is his heat sinks. I do not know anything about his PMD's extensions or resistors. I buy those from Leroy

You could still have a harness issue or as you said an ignition switch issue. I had one bad pin in a harness that gave me fits until I found it. That was on a fairly new harness that the PMD plugs into

Actually a #9 does little to nothing, it is a calibration resistor tech use following a rebuild of a IP 1-9, #5 is what they use when new as it is middle of the range as you go up you add 1mm fuel for #6, 2 for # 7 up to 4mm max. numbers below reduce the fuel by 1 as numbers get smaller.

Again this is a CALIBRATION RESISTOR use to set flow on a IP test stand where you rev IP to a series of steps to full speed then you measure the volume of fuel delivered, if it does not fall into test spec range then you swap resistors.

Now at WOT APP all way to floor you MAY , MAY, get a slight bump in fuel contingent of wear in the IP already, if your IP 'innards" are wore out then evan a 9 would not add any appreciable fuel.

Now once the WOT demand has been met then the PCM will cut back fuel to the programmed fueling tables, since IP is metering fuel to/from vs PCM wants the extra fuel disappears once achieving demanded speed setting.

In the OBD-1 generation trucks the resistor can be pulled and PCM will run on stored value until about 50 start & warm up cycles then it will default to base setting of a #5 resistor. (So I have been told), I don't own a OBD-1 so I can only "parrot" what others have said back in the day.

I do own (2) OBD-2s both 98C1500 Burb and a 98 K1500 truck, those I do have factual knowledge of, they will run at previous stored value if resistor is pulled indefinately I ran mine for 1 year as part of a R&D experiment to prove that the "variable fuel controller" available at A-1 Crapstoms site is pure junk as is most of his "expertise" for the 6.5.

If you do a TDCO offset learn on your OBD-2 truck and no PMD resistor the PCM will "see the resistor is missing" set a resistor code and then give you a no start condition until resistor is reinstalled?

My point of experiment was as I knew, that adding a potentiometer into the signal of the fuel solenoid does "NOTHING" it does lighten your wallet, if you want to do that I'll send my address and you can send me the $$$ and get the same result you would have buying A-1s junk.