Thanks for posting. It sounds like you have a decent handle/assessment on what your areas of strength and weakness are. You are a somewhat 'older' than average applicant but less so when focusing on part time or online programs. Yes you should focus a lot on that GMAT!! Especially to help somewhat overcome that lower GPA. And yes if you were able to enroll in a course, particularly a relevant quant or business course that is graded and get an A (or two), certainly that would be a plus.
Haas would be a stretch. UCLA could be a bit more reasonable as they have a much higher acceptance rate for PT; with a strong GMAT. Online programs would likely be fairly within-reach in many cases. The other schools you have mentioned sound reasonable. Not sure if you are considering USC Marshall but their part-time program has a high acceptance rate. You could also look at UC Davis among others.
Focus on what you CAN still change-- namely the GMAT and your essays!
Keep us posted on questions and your progress, good luck to you!
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