I have checked and checked for vacuum leaks and found none. I sprayed Carb
cleaner all around the intake system and got no indication of a leak.  Could
not spray directly under the air plenum though.

Well, I took the intake off and put it back on (I still think I might have a
leak in the center plenum) and gained over an inch of vacuum and the engine
runs better.

So, If you have checked and replaced parts, check you vacuum and if it is low
take the intake system off, clean it up and put it back on and see if it
helps.

The plastic gaskets at the head under the air runners can get brittle and the
paper part get dry and allow air to leak in creating running problems.

The rubber boots connecting the center plenum and the air runners also can
leak causing problems.

Engine runs cooler and is a little more responsive the throttle now.

Robert