Sputtering sputters at high speed. leveling off at 65-70 mph sputters badly.excelerate and it smooths out. misses bad 45-50

You make no mention that you have had a fault code scan run, do that first.

to me, it sounds like fuel related problem.
Clogged fuel filter, bad (aged) fuel pump, or water in tank.

one thing I doubt is "Sputtering".
low fuel pressure don't do "Sputtering".

Hi T:
Interesting as smooth idle and sputter are contra-indications.
- Smooth idle should be healthy
- Sputter could indicate problem:
- mis-fire? Possible bad spark plug or bad exhaust valve. Pull spark plugs to check to see if any are fouled. Compression check will help depermine why fouling is happening.
How many cylinders?
How many Km on engine?
With engine hot, Remove oil filler cap and see if any vapour indicating blow by (bad rings)
My suggestion?
Do some more checking and reply as a comment on this post. Will assist if I can.
Cheers.

bad coil packs

EGR Valve or more bad coils

Try putting a professional scan tool on it
using Mode #06 or walk a new coil until you
get the bad one

Does it use spark plug wires or individual ignition coils for the each plug?. My 98 intrepid uses coils and occasionally I have to change them out cause it would start to miss when normal temperature was achieved. If it uses wires, try replacing them, along with the spark plugs.

check tune up if done or not needed is engine on check egr system

You may have a bad furl pump or bad fuel injactors

Sounds like a bad coil-pack

check computer for mis fire if this shows up suggest a tune up be sure to use dodge parts (tune ups with after market parst dont seem to last long)