i have a 89 firebird 2.8 fuel injected. my car will run pretty much fine if i dont give it much gas under load but say i punch it it will start missing like crazy. but when its in park i can rev it up and it will run fine. i have jus recently changed all the plugs and wires, put a new air filter in it, and changed the oil. also after about 20 minutes of driving around the oil pressure likes to drop down to about zero. i cant figure it out

 

What plug gap? Did you inspect the distributor? Test the coil(s)? The description is much like a weak ignition system.