My gosh man, you have the exact same symptoms I'm experiencing, minus the high temp issue. I am noticing one thing that wasnt there before, a fairly loud gurgling sound coming from the pass side dash. I just had the coolant system flushed and refilled recently for high motor temps and it made the sound just before i had the flush. Does that tell you guys anything?

BTW I don't mean to piggyback on your thread but I'm hoping this could help me out as well.....

 

Hey Siscokid---I have the same gurgling sound too. My buddy who helps me w/ mechanical things w/ the blazer said there was air in the system and has to do with the heater core. But since the heater core is still functioning, leave it alone cuz the heater core replacement is a real pain. You have to remove the dash and everything.

 

top off your coolant again.

 

I THINK I FINALLY FIXED THE PROBLEM!!! (miss at 60 to 70 mph) yesterday I installed a fuel injector spyder assembly, if your thinking of doing this Rock Auto has a great price, $294 for AC Delco unit and it came with all the required gaskets and bracket. I took my time at disassembly, lots of carbon under the air plenum, found a small nut, #10 maybe, between the plenum and the intake seal, I believe this has been apart before. I cleaned the top of the plenum and also the intake with carb cleaner and then cleaned the underside of the throttle body with throttle body cleaner, both required the use of a small brass bristle brush to clean away all the carbon, once clean I noticed the dist. cap seemed loose so I replaced that and the PCV just cause it was easy to do, I did try a very thin coat of RTV seal where the dist cap meets the dist. never tried this before but I have alway thought that moisture was getting in there. Total job took me about 4 hours but it sure runs better, smoother idle, better pickup and hopefully better gas mileage(we'll see) but best of all the miss is gone.
Thanks to all for your suggestions. AMXAL