Car-89 2.8 firebird
Symptom- idles @ about 1100, revs fine with steady throttle up to 2800+/- then completely drops off, spits out copious amounts of white smoke then mellows back out when the throttles closed again.

Checked-Timing, 10* though most of the time it retards slightly upon opening the throttle before advancing?, Fuel press & compression both well within specs, no oil/water loss no overheating or fluids from the tailpipe, recently changed intake gaskets, o2 sens, plugs & wires. cap looks good buttons clean, fresh ect, icm, pickup coil and pass. donut (drivers side is shot could this cause any issues aside from heat) fuel pump, tps, iac, oil press sender are all within about 2 yrs old. only guage test ive found bad is my vac hold a steady around 5in timed at 10* and a steady 10in timed closer to 12*

Any help you all could give me or ideas to throw out would be much obliged, I've drove this thing with plenty of power daily for 3 yrs (although i bought the vac guage in feb and it always held slightly low but was always steady and built back up when opening the throttle pretty quick now it doesnt build back up at all) shut it down at a gas station was runnin great, went to start it back up and she wouldnt.

 

Your engine vacuum sounds low, are you testing it after the throttle body or on it? It should be closer to 16".
Does yor timing advance when you rev it?
Check all the grounds, esp. the ecm grounds.

 

Testing the vacuum off the small nipple on back of the plenum, the timing advances when it revs but on the initial opening of the throttle it retards about 2-4 degrees, advances up til it hits the upper 2k rpm's and then retards back down to about 10*, wasn't sure if the 2.8's have knock sensors, i did find a pigtail plug ill post a pic of while checking grounds, its only two wire and runs in a set of wires alongside my fuel lines on the driverside of the engine bay, but its plugged into nothing, has a small resistor spliced into its two wires, ohmed the terminals on it one has no resistance to ground, bout 500 to hot and vice versa