I didn't ever deal with the VP44 Dodges too much but my gut says there is a quirk with the injection pump, which may or may not fix anything, and get expensive. I don't know how much you can see with a scan tool on those trucks but it might be worth having a look at what you can see with one.
VP44 failure is usually preceded by in-tank lift pump failure. I will not operate a Dodge of that vintage (including mine) without a fuel pressure gauge. I also have an aftermarket lift pump (AirDog) mounted under the truck on a cross rail.
(There's a few different good quality brands. They're all nearly bomb proof and guarantee you'll never starve the VP44 of fuel. Some like mine also include a fuel/water separator and another level of filtering prior to reaching the stock filter/separator. Some companies suggest removing the stock filter/separator when adding a pump like mine. I do not. Because there's also a fuel warming device in the filter/separator for winter driving.)
The VP44 is cooled by fuel and when the lift pump in the fuel tank fails, it cascades into killing the VP44. You must have 5 psi or higher feeding the VP44 under load or it's going to fail quickly.
And even at that, the VP44 will eventually fail. They all do.
Mine grenaded pulling the fifth wheel in Nebraska on a hot day headed for OSH a couple of years ago. $2000 for the VP44 and labor, and I was on my way again in two days.
I had the standard mechanical failure. The stator seizes and the impeller snaps off inside the pump. The other failure mode is the computer that sits on top is susceptible to heat cycles and can fail.
Anyway back to the problem at hand...
That sound sounds like fuel flow to me. But there's some different possibilities as to why.
I'd get a fuel pressure gauge on it quick and see what it's showing under load and at idle. If it's the lift pump you might save the VP44. With my aftermarket pump I won't settle for anything lower than 13 psi feeding the VP44 but that's overkill.
That's ONE possibility. How does it run when it's warmed up? Surging go away under load or once warm?
If it's not throwing codes, more likely, and if the injectors are original, is you have one that isn't pooping off at spec anymore and it's creating a misfire.
Injectors can be removed and pressure tested pretty easy. Bit less spendy than replacing a VP44.
But I don't think the surging you're hearing matches an injector problem unless the computer is having trouble compensating for it.
Any extra smoke from the tailpipe?
Unlikely it's related to the grid heater if you see and hear it cycling. (Even in a truck with a solid electrical system, that bad boy draws a LOT of amps and you can see and feel and hear it cycling at idle from a cold start. It'll cycle until a couple of different parameters are met and the engine is then considered "warmed up".) Grid cycling sounds and feels lot like an air compressor cycling in summer.
Loads down the engine a few RPM, headlights and dash lights dim a little when they're on, load goes away (alternator) when they're off. Goes back and forth until the truck comes up to temperature which takes about two miles of slow driving or a mile of normal speed driving. It'll never warm up at idle unless you have an exhaust brake and activate it to get some load on the engine.
Other stuff it can be: Bad TPS sensor or camshaft sensor (usually causes problems above idle but not always on the TPS sensor - sometimes they develop a dead spot near idle and their output is erratic telling the truck that your fiddling with the pedal when you're not). Again less likely but it happens.
Another possibility is there's a Fuel Control Actuator (FCA) that's on the VP44 that's replaceable that can go bad and surge the truck by not responding correctly to the computer controls also.
And finally: Check for a cracked fuel line. Sucking air in will cause surging also.
Could be a lot of stuff but it sounds like fuel to me.
@gkainz turned me on to one of the best Dodge Cummins people I've ever met here in Denver but I don't know if he could do the diagnosis over the phone. I bet he could give the absolutely most likely things though. Give MaxTorq Diesel in Golden, CO a call and send them some beer money if they're right. Rob and Dawn are great.
I see some monkey gave them a bad review a month ago on FB after blowing up his engine.
Wonder if they've noticed.
Would love to hear their side of that story, considering they rebuilt mine and studded it also and it's been a freaking tank since then, and Rob was very careful about the boost level on mine since he knew I was set up for and needed to tow heavy, not race.
got around to "check the simple stuff first" with the fuel filter and Water In Fuel separator.
