I know what you are saying about the fuel grade, was running 87 more often then not and i am sure it had something to do with the original motor failure.
The stumbling, I have going under hard acceleration seems to be ignition related. Today, I changed the plug wires and did away with the heat shields around them. Also I have been running 93 in it with a bottle of Lucas fuel system cleaner,can't hurt right? Now it is running much better. It will still stumbles or hesitates a little now and then but nothing like what it was doing before the wire change. The car gets up much better now so I think I am the right track. I am thinking, maybe, pull them $50.00 plugs out and trying something else. Any Ideas what I should try?
I will check the fuel pressure and the misfire counts when I get a chance to get to the GUY with the right tools for that check. What about this ICM? Would this have any bearing on a random hesitation under a load like this?
I going to keep pocking around and changing out things, seeing how I have my old motor (that didn't have this weird problem) and everything on it is good except for the ugly #4 cylinder.
Keep the ideas coming and I will let you know what I come up with.
Thanks All and Happy New Year!!!