My son's 2010 Ram 2500 is misfiring on cylinders 6,7 and 8. The oil filter adapter was leaking, so I though maybe it was due to oil pressure but once replaced it's still doing it. Where do I go from here?

Pull the valve cover and be sure the push rods are still in place.
After my son and his buddy went through hours of the scan testing, coil replacing, and wire chasing, they pulled the VC and found a pushrod out of place. Fixed that and the misfire went away.

Sound advice right here. Fortunately you got a cylinder(s) code. On my vehicle I did not, but after popping the first valve cover the problem was apparent. #8 cylinder exhaust valve spring broken. Springs and rods are common failure points on these. If you do have to replace a spring, buy the tool. Its a 10 min job.

Flat cam lobes are a very common problem also.

2010 is most likely A. bad cam or B. broken valve spring and I have seen both on the same engine at the same time.

The truck only has 84k miles. We hade the heads off and inspected the cam and heads and there were no problems.

Try swapping the coil packs with other cylinder coils and see if the misfire follows the coils to the different cylinders.

Did you do a compression check before you pulled the heads?
I'm sort of wondering why you started by pulling the heads?
Did you do other tests before you pulled the heads?
Change the exhaust manifold studs while the heads are off.

I chased a pretty bad misfire in my old mini van. Turned out to be bad injector seals. I replaced everything I knew to replace for a misfire before taking it to the dealership and being told it was $8 in parts to fix it (after spending a couple hundred).

Mileage is irrelevant with these new engines and their specific problems

The heads were pulled due to broken exhaust manifold manifold hardware. All the hardware was replaced along with the manifolds.

The engine ran great before the heads were pulled. No check engine light or anything. I don't have a way to check compression. I have a compression tester but it's not long enough to get down the spark plug tubes.

Now you say it developed this after they pulled the heads. Massive vacuum leak.

Duffman- any hydraulic shop can make you what you need very inexpensively. I also know for a fact autozone and advance auto sell the adapters for 1/4" npt thread.

But where? There isn't many places for the engine to pull in vacuum.

I ordered a new compression tester from Amazon that includes a bunch of adapters as well as an extension tube that should work.

I finally got around to doing a compression test. All cylinders are 175-190 psi which I think is reasonable.

On thing I noticed is the battery is only putting out 11.5 volts, but once it’s started the alternator is putting out 13.7. Those numbers seem low to me. Could that have anything to do with it?

What’s the common denominator between cylinders 6-7-8 that would allow for a misfire?

Pull the spark plugs and inspect them

The plugs if destroyed mean the pistons broke

If not it’s a wiped cam lobe or three. I have money on the broken piston

We had the heads off, no broken pistons, inspected the cam and the lobes look fine. This is a 2010 Ram 2500 so no MDS, so it shouldn't have the cam problem.

It runs fine at high idle, then starts missing when it drops to low idle. It's not firing because the exhaust is rich. We've moved around coil packs and it still misfires on the same cylinders.

Do a running compression test and report back

As I stated before; I did a compression test and all cylinders are 175-190 PSI.

I have replaced a ton of bad cams in 2500 5.7s without MDS, the MDS is absolutely 100% NOT THE CAUSE OF THE BAD CAMS!!!!