k guys....i need some help

now i'm just a starting mechanic here ....but i do know quite a bit of stuff....i just want to know where to start with this one cause i don't want to replace good components

when i got my 86 trans am it threw so many codes it was rediculous....but my mechanic( since i was interested in auto mechanics at the time i didn't know anything) fixed most of them over time...but i am left with 2 codes....and the only time the light comes on is after about 30 minutes of freeway driving...never at lower speeds....i do have an exaust leak that i've been meaning to fix...its before the cat. .....that area up there
that 2 codes are

32. Fault in barometric pressure sensor circuit OR
Fault in exhaust gas recirculation valve diagnostic switch OR
Fault in electronic vacuum regulator valve
33. High voltage (low vacuum) at mass air flow sensor (or MAP sensor)

i need some suggestions on where to start testing( i've taken auto electrical theory....so i'm not a complete idiot!

thanks guys!!