I need help from anyone who may have had a similar problem or has a clue as to why my altima is having this problem

The Problem: Of my 4 non-continuous monitors, 3 of them are reporting as not-ready (the catalyst, oxygen sensor & EGR system), the 4th (the oxygen sensor heater) is reporting as ready. All the mechanics I'v talked to said that all I had to do is drive it 50-100 miles to reset the drive cycle, and this should fix the problem. I've driven it hundreds (close to 1000) miles and the problem still won't go away.

Does anyone know what is going on?

(Info: the car is a 97' Altima GXE, 5spd 2.4 liter)

UPDATE: They tried to run the codes, but said the ECM wouldn't report the codes. The dealer is saying that means they need to replace the ECM for $1200! Another mechanic is saying its just stuck in a closed loop and it is probably the oxygen sensor. Any opinions?