This 3.1L engine has 194K miles on it and no major repair work done on it. Recent compression test showed low 190's across back bank and upper 160's across the front bank of cylinders. New spark plugs, plug wires, EGR valve. Acceleration is good from standing or any speed.
Idles rough at stand still and at any cruise speed, although >50 mph is worse. Have checked all vacume lines and no leaks detected.
Anyone have any suggestions?

try some injector cleaner

Could you do a vacuum test ( one at idle and one at 1500to 2000 rpm's ) and post the results and that will help diagnose your problem better . Yes injector cleaning would help if it's not already be done .

I'll get a vacume test done next.
Had trouble (similar) at about 90K and replaced all 6 injectors, fuel pump, filter - so learned my lesson and now only burn 87 or 91 oct. fuel from Chevron or Texaco - with bottle of injector or fuel system cleaner about once a month. Somehow this just seems like some other problem ---