Can i take mucinex dmv and 5 hours later take promethazine dm?

No: Dextromethorphan has never been shown in studies to relieve any symptom of colds, flu, allergies, bronchitis or pneumonia, including cough, and can be dangerous in high doses. If you have thick mucous, use PLAIN guafenesin (Mucinex). If you have nausea or a cough use PLAIN phenergan, or (for cough) phenergan + codeine or hydrocodone (but you will need an rx for phenergan + anything).