Extreme Hesitation at Acceleration...

My 90' GT just started balking badly, when the pedal is pushed over the ~60% point. If I stay under that point, the car accelerates like the typical monster that it is.

Anybody else experienced that?

Not personally, but as the intake is a dual plane plenum (as I recall) that is affected by a component known as the flappy valve, that is where I would start.

Here is a link to consider: www.nichols.nu/tip437.htm

Did it start doing this all at once?
how long has this been happening?
Has anyone touched your timing or had a sharktunner connected?

Could be MAF...

The car had been running perfectly, with nothing being done in a while, other than normal oil changes. Then out of the blue, my Smog Pump locked up, about 6 months ago. I ended up leaving the belt off and have been running without it (since advised by numerous folks that it is really no longer necessary). The car ran fine after that, for half a day. I was on my way to get fuel (since I was really low), when everything went to hell. The DTE showed 16 miles remaining, which I'd never gone down that low before. (in retrospect, I could kick myself for that one!). But it died and would only crank, run about 10 seconds (horribly), & then shutdown. I ended up getting towed home.

So 6 months (and a much thinner wallet) later, I have done the following to try to resolve:

- Cleaned the MAF with MAF Spray (some have scolded me for this already, since they say it cleans automatically by burn-off)
- Cleaned the Throttle Body
- Replaced Spark Plugs (Bosch Platinum 4s)
- Replaced all vacuum line elbows (that were visible above Intake)
- Replaced Ignition Wire Set (Beru OEM set)
- Replaced Fuel Filter (Bosch)
- Installed Fuel Pressure Gauge (to monitor pressure, which is fine)
- Cleaned Exhaust Temperature Sensors
- Replaced Air Filter (Mahle)
- Replaced LH Relay
- Replaced Fuel Relay
- Replaced Ignition Relay
- Replaced Coolant Temp Sender
- Replaced Temp II Sender
- Replaced Fuel Pressure Regulator
- Tested Fuel flow (45oz out of pump, in 30 sec) which is fine
- Reseated and cleaned all Fuse and Relay contacts

Yet the problem is ongoing. I can't afford any more downtime, so I just ended up dropping it off to Howard Wright at European Classics of Atlanta. I am betting he is going to find something wrong under the Intake, which I have never had off.

Holy crap Kent, That is a lot of coin to throw at guessing what is wrong.
I hate when people do that and then bring me the car because now I have to keep in mind every thing they have touched (for future reference)

You Installed a Fuel Pressure Gauge (to monitor pressure, which is fine)
that was a good step as well as checking fuel flow.
I just hate to touch anything until I find something actually wrong.
Well I am guessing that the guys you took the car to will find something wrong under the intake and you will be able to tell us what happened