A gutless 94 gt! Here are the codes... What do you think?

try cleaning the mass aif flow sensor a dirty mass air will cause it to run lean.

Usually a lean code for both banks isnt the O2 sensors. I say usually because in some cases it can be but its rare for them to both go at once so you would have had to have been driving around with a bad one for a while. Since you dont drive it a lot however it could be possible. Anyways getting back to the vac leak. A couple of the things you described doing to your car could cause a vac leak and the lean codes. Especially the whole forcing the EGR back into place scenario. I just had a kid at my work who had an intake off a Taurus 24 valve motor and once he put it back together it came back the next day with lean codes on both banks.He chased his tail for 3 hours taking the intae on and off, replacing the o-rings etc. I figured it out after about 5 minutes with a can of brakleen. Spray it around on suspect areas and if theres a vac leak youll hear the idle kick up a bit while it burns the brakleen making it rich. Long story short when he disconnected theEGR valve the gasket fell out and he had a vac leak. If you can access PIDS with a datalogger on an OBD2 car you can have someone watch the PIDS while you spray around the egr valve, and around the intake seals and vac lines, etc. Theyll be able to see a spike in the upstream O2s when you hit the vac leak. And also, if you do have an OBD2 car, and can access pids on a scan tool, look at the fuel trims for banks 1 and 2 and if you momentarily gowide open, the fuel trims should drop down to normal levels because vacuum is low. I didnt happen to see what year your car was because Im using my PS3 and I can scroll back or Ill lose all I just wrote.

Just re-read your post, 94 GT. I guess that negates all the PID monitoring... You should still be able to hear it if you hit a vac leak with brakleen. Just dont do it while the cars really hot for obvious reasons...

here's a write up i did awhile ago:

to check the EGR valve:

bring the engine to normal temp.
connect a vacuum pump to the EGR Valve
apply 5in vacuum to the valve.
if engine stumbled or died then EGR Valve and passage(there is a passageway through the intake and tube coming off header) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled, connect vacuum gauge to the hose coming off of the EGR Valve
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?

if not, check for manifold vacuum at the EGR vacuum valve.
if you have manifold vacuum then connect vacuum gauge to the EGR valve side of the vacuum valve and snap throttle to 2500 RPM.
should read about 2-5 in minimum vacuum