oh well.. i've got the same prob here.. all my other cities i hav a rating above 100 (127 in one), and i was proceeding the same way for this city... the thing i see same in our ptoblems is tht they request an airport, and also i believe commercial demand is very high... could that be the reason?? more commercial zoning required?
my rating also went the same way... from 100 to -60 in abt 3 to 4 years... i restarted the city after makin a backup.. and that dint help one tiny bit...