1998 Chevrolet Other Idles rough and then stalls

1998 Motorhome on a Chevrolet P32 chassis, 7.4l 454 vin code B, 15,000 miles. At highway speed runs fine, plenty of power, no problems. Stop at a red light rpms fluctuate 300-400 rpms and will stall if I do nothing. Put it in neutral give it a little gas and it runs fine, no rpm fluctuations, light turns green, let off the gas put it in drive and it runs fine. First start up in the morning no problems, let it idle for 10 mins and the rpms start to fluctuate and will stall unless you give it a little gas, always starts right up after it stalls like nothing was wrong.

Since this started I have changed the in line fuel filter, plugs, plug wires, dist cap, dist rotor, PCV valve, EGR valve, IAC valve, gas cap, MAF sensor. Removed and cleaned the throttle body.

I checked and had a technician check the vacuum lines, engine and chassis grounds, fuel pump pressure was 50 psi, tech hooked up a scan tool, no codes and parameters all looked normal to him.

Put Lucas tune up in a bottle (x3), 75 gallon tank, and a full tank of premium gas and drove it 400 miles, still doing it.

Of note, the tech pulled the plug off the engine coolant temp sensor and the idle smoothed out, not perfect and took longer to stall, he also sprayed either carb cleaner or something similar into the air intake box with the engine running and the idle would momentarily smooth out.

I understand that pulling the plug on the coolant temp sensor makes the computer give more fuel just like me manually giving it a little gas thus making it idle better.