I replaced all 6 plugs this morning and the problem is improved, it no longer stutters at 40 mph when getting up to highway speed, but there is some "fluttering" around 55-60 with rpms near 2500-3000.

If I put my foot through the floor, it pulls good and strong and there is no staggering or fluttering.

Attached are the pics of the plugs that came out of the engine after 126K miles. I suppose I'll do plug wires next.