1995 Concorde warm up difficulty

My 1995 3.3L Concorde starts fine and runs perfectly when warm, but for
several minutes during the warm up it has a power problem.
This occurs a few minutes after starting, from a cold overnight start or
from a few hour stop. After several more minutes it will be OK.

It starts running rough, missing slightly, doesn't respond to the
accelerator and has backfired when I push the accelerator hard on a hill.

BTW I replaced the EGR hoses and valve about 6 months ago. The hoses had
disintegrated, but the valve was still in reasonable shape. The spark
plugs were replaced at 60K miles.
This engine is in very good condition, only about 85K miles with oil
consumption and fuel mileage as when new.

Hopefully one of the experts here can put me onto the solution.