My only experience with a stuck injector was one stuck open on a Gehl skid steer. The symptoms were that it idled normally but knocked and puffed white smoke at higher power settings. I took that injector apart, cleaned it, put it back together, and all was fine again. An injector stuck open will start injecting the fuel early and at high power settings will inject too much fuel. I have not heard your engine but it seems like an injector stuck open could give you the symptoms you are having. I suppose a damaged nozzle could as well. My line of thinking does not exclude a VP44 problem but cleaning/replacing an injector would be much cheaper and easier to do. I hate to mention it but it is possible that an injector is stuck open because trash coming through the VP44 (like metal filings from a mechanically failing VP44). I would be inclined to play with the injector first. If you swapped injectors with another cylinder and the cold exhaust port moves with the injector you would know it was the injector. If the cold cylinder does follow the injector then it is either the VP44 or a compression problem. With the right gauges you can check the compression in all cylinders through the injector ports (injectors removed).
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96 3500 4WD, 47RE, gauges; 97 3500 4WD 47RE, gauges; 97 3500 2WD 5-spd; all club cab. 98.5 2500 2WD SB, 5-spd, gauges, quad cab