Truck is a 2000 ZR blazer with just a little over a hundred thousand miles. It has a strong mis/heisitation when the throttle is opened part way(2000-2500 RPMs). When at WOT it runs smooth again. It also starts and idles fine. The problem usually goes away (or gets better at least) after its driven 8-10 miles. No check engine light, or any codes to retrieve. Here's a list of what has been replaced within the last 3000-5000 miles. (not listed in the actual order of replacement)

-Fuel pump-Delphi (pressure was within spec. on old pump, but sender for fuel gage wasn't working anyway
-MFI conversion using AC Delco spider assembly
-Fuel filter-Napa
-Spark plugs, wires, distributor cap and rotor button-Carquest parts
-Ignition coil-Napa
-Cleaned MAF sensor
-TPS and IAC-whatever they sell at advanced, BWD I think
-Map sensor-AC Delco
-Pulled and wiped off crank sensor
-Cleaned all grounds and reinstalled using dielectric grease
-Entire exhaust is new after manifolds(Y-pipe.cat.,muffler,tailpipe)

For some reason I can unplug the map sensor and the symptoms all but disappear. Make any sense? Also the inside of the muffler sounded like it was sizzling after I shut it off the last time. It was not glowing red and didn't seem to be giving off any excess heat, but it didn't sound "normal".

 

Sounds after you shut off the vehicle are fairly normal due to the expansion caused by the heat of the exaust.

As for your hesitation, my first thought would be the ignition system. Does the hesitation only happen in the morning?

Take the cap off and inspect if for any hairline cracks or excessive "white" carbon corrosion on the contact points.

Edit: just thought of something, is it a sizzling sound or a random pop/crackle sound. I get a pop/crackle sound. Sizzling at the catalytic converter could indicate a clogged cat and could be a cause for the hesitation.

 

The sound from the exhaust that I heard yesterday was coming from the muffler and it was not the typical hot exhaust, pop/crackle sounds. I was racing the throttle quite a bit, so maybe it was just a bit hotter than usual.
Yes the hesitation issue is typically in the morning only. I've owned the truck since it had 67000 miles and it now has 101,000. At about 70000 I changed the distributor cap,rotor,plugs and wires. At about 95000 I did them all again even though nothing looked that bad. I will pull the cap off again tomorrow and inspect. You're probably thinking moisture is getting in there as I thought this before too. I'll report back if I find anything. Thanks.

 

mine is the same but it happens all day, mostly when you first start driving.i also unplugged the maf ,the problem is gone.would that mean the maf is bad,or ??