If this is a true pre-approval then your loan should have already gone to the underwriter. Is this a prequalification based on credit being pulled? It doesn't sound like you should have any problems as far as credit. If this has not gone to underwriting yet then my guess is they may ask for a couple of more verifications, such as utilities, cell phone, insurance etc, showing no late pays
EQ 778 EXP 782 TU 729