Rpm related vibration 5.9 magnum

If it's popping in the pipes, it's either
1) the timing is extremely unstable,or the plugs are sour.
2) engine is lean
3) sloppy spring pressure.
4) contaminated fuel
5) headers sucking air at the head flange.
Fix the popping first, then attack the vibration......which may or may not be related.
If the popping occurs at the same rpm whether loaded or in neutral, it's probably ignition related (could even be the tach)
If it's related to the engine load, it's probably an air/fuel issue.

1) unstable timing is easy to see on the timing lite.Sour plugs are not. But can be inferred by reading them. If they are white or yellowish, not new, and shiney, as in glazed, I would start by replacing them and fattening up the low speed circuit. If you have been tuning the low-speed circuit with an AFR gauge, STOP!
2) is an easy cure, unless the emulsion tubes are involved
3) I doubt this one, but you never know....
4) and 5) you can test for.

As to lean; This can be not enough fuel.... or....... too much air, so you gotta do your due diligence testing every device attached to manifold vacuum and all their plumbing.
I'm guessing 2500 is near cruise rpm, so the throttle valves are probably gonna be at the top of the transfers or slightly into the mains. So if you get into the carb, you are gonna have to check out the low-speed circuits.

Here is a test
Keep your eye on the temperature gauge, throughout the test. If it changes, the test is VOID.If the rpm changes with or without the air filter house installed, it may be the fan blowing across the bowl vent, or the vent too close to the top of the lid;so you have to keep that in mind.
Here we go;
Block the throttle open at the rough spot, using the fast-idle cam and it's speed screw, or whatever it takes. Grab the distributor, and change the timing in whatever direction it takes to reach a maximum rpm, then reduce the rpm back into the rough zone, with the speed screw. Now adjust the low-speed mixture screws to obtain the highest rpm, and again reduce the speed into the rough zone.
If it's still rough grab a shop towel and slowly cover the secondaries.If the rpm changes,stop the test and close the secondaries all the way. Then resume the test; readjust the mixture screws and retest the secondaries with the towel. After the secondaries stop messing up the transfers, bring that shop towel slowly over the primaries. If the rpm goes up, she's lean . If down, she's either right on or a bit rich. To find out which, clamp the fuel supply line, and wait .
Pretty soon one of three things is gonna happen;
1) the rpm will rise, level off, then fall to a stall.This started out as too rich, then perfect, then ran outta gas,or
2) the rpm will immediately begin to fall, and then stall. This is lean, or
3) The rpm will do nothing for 5 to 8, or more seconds, then begin to drop to a stall. This was perfect, then went lean and ran outta gas.
Awright kick it off the fast idle and let her cool for a bit, then fix whatever needs fixing.
But if you got a #3, there's more digging to do.And the first thing I would do is replace the plugs,and start the test over.
Good luck.

Oh yeah, put the timing back or recurve your D

done