Truck stalled and died while slowing down

[CajunAg]

Greetings all. I have a new-to-me 2020 Ram 2500 w/ 6.4 Hemi I bought in CO and drove home to Southeast TX. Between the trip from CO and driving it around town, I have put about 2000mi on it w/o any incidents. A couple of weeks ago, after I left the house and was slowing down at the first light on the way to work, my engine started shaking hard and suddenly stalled/completely died. I put the knob back into park and tried to restart it, it would turn over but wouldn't start. CEL wasn't on at first, but came on when trying to restart. An hour later when the flatbed arrived, I did manage to start it but the idle was very very rough. Flatbed got it to the dealer, and just last week I finally got a diagnosis of sorts. The No. 6 cylinder had low compression, and the dealer Service Writer is saying they need to replace the left side engine head. Apparently the engine head showed signs of overheating, prompting the replacement. He didn't give me anything more specific than that, they are installing the new head now and will see if that fixes it. The truck is still under full factory warranty, thank God, so Ram is eating the costs, but does that overheating diagnosis seem plausible? The truck had 22.5k miles when I bought it, so it's currently around 24.5k. It's been babied since I bought it, no towing, no heavy payloads, just short (12mi) commutes. When it stalled, it almost felt like the engine was stalling as if the transmission was a manual and the clutch wasn't depressed. It didn't buck the truck, but it was a very strong vibration. It was also a hot day, but no hotter than the previous weeks have been lately. Has anyone had a similar experience or suggestions on what else to ask the dealer to check? TIA

I also asked the dealer, just to be sure, if there was some sort of tuning that needed to be done to adapt the CO truck to SE TX, but he said I no. I figured the modern engine management systems can handle changes in elevation/temperature/humidity automatically, but I wanted a definitive answer.

 

[flan]

I can’t seem to make their theory work in my brain at this hour but sounds like they must be on to something to get warranty to approve the repair. Let us know how it goes.

 

[CajunAg]

Welp, 38 days at the dealer later, I finally got my truck back. Official diagnosis on the work order is that the exhaust valve spring broke, which in turn damaged the exhaust valve and valve seat in the head. I assume the damaged valve seat is what prompted the head replacement, but it could have been from other damage when the spring broke. This was seemingly what caused the sudden engine stall when I was stopping. The "signs of overheating" issue apparently stemmed from the discovery of coolant in the EGR valve/system, which wasn't related to the exhaust spring/head issue. Dealer replaced the EGR valve and cooler, along with a fresh seals for everything replaced and an oil change. Everything seems to be in working order now, hopefully the bad spring and the EGR valve/cooler was just a random statistical one-off and not a sign of a bad batch, as I haven't even quite hit 25k yet.