I would check to see if the 1992-1995 style dual valve EGR system is working properly.
It is very common on older OBD-I system Ram pickups for the seat sealing surface of the EGR pintle valve to corrode away badly and allow extra gas flow all the time.
Since the EGR valve on the intake manifold and the loose EGR modulating valve are both hard to get at in their positions in the rear I would just buy new ones and install if the ones there are old. Check for brittle plastic vacuum lines too.
Do not just disconnect the electrical plug to the EGR modulating valve or the separate EGR valve, doing either of those turns the EGR flow onto maximum causing stalling.... this was an EPA "fail safe" rule.
You could disconnect and plug the hot gas line from passenger side exhaust manifold up to the EGR valve to see if the steady speed bucking goes away. Both threaded connections are likely to be corroded so use Mopar oxygen sensor thread spray, Kroil, or your favorite penetrent. Just cutting the steel tube and using hi temp silicone hose to rejoin is an option.
Below the throttle body butterflys is a cast in EGR passageway with dual outlets aiming right and left. One of these two holes can plug with carbon deposits, causing all the flow to go to 4 cylinders.
Dirty fuel injectors causing multiple cylinder misfire from lean a/f is also possible.