To get the maximum DTI of 45%, you need following
(1) excellent credit score (2) enough income; AND (3) meet the reserve requirement.
You cannot quit your job and lose (2) in order to meet (3). They needs to be true at the same time.
"For manually underwritten loans, Fannie Mae’s maximum total DTI ratio is 36% of the borrower’s stable monthly income. The maximum can be exceeded up to 45% if the borrower meets the credit score and reserve requirements reflected in the Eligibility Matrix."