I ran my last 5.7 Durango to 165k. Performance and oil consumption were as new. My current one has about that and I plan to go to 200k at least. Both needed a water pump around 140k. The prior needed a fan clutch. The latest needed an exhaust manifold (warped) around 100k. That's it. The 5.7 seems to age very well.

A Magnum, driven reasonably and maintained, should do better as there is less load. There will be more maintenance at higher miles but I think no basic issues with the engine.