The school I want to attend doesn't require PCAT (they don't even report the average score), but I think if I take it, I can score in the 90th percentile+
The vast majority of programs no longer require the PCAT with plenty of others not even looking at it as part of the interview process.
Would failing so many classes in med school be a red flag?
This is a red flag for any career change in healthcare, but by all means it does not warrant a screen-out for interviews. Especially for pharmacy.
I eventually did pass some of my classes after remediating, and many of the pharm classes seem to be on topics we've gone over in med school (i/e: Infectious diseases, Biochem, Hematology, Neurology), so I feel prepared since I've seen the topics before.
So, albeit you may have been introduced to pharmacology, you will be going beyond the surface (8 semesters) of pharmacology mingled with therapeutics and pharmacokinetics. So yes, to incoming students you've been exposed to more, but the goals of both careers is vastly different.
Also, unlike med school, which was pass/fail, pharm school is graded, and one needs at least a 2.7 GPA to graduate, but I want to get a residency so I'm trying to shoot for a 3.5.
I wouldn't necessarily get the 8-ball out and predict a residency with hospital placement just yet. The vast majority of jobs are in retail and regardless of if one does a residency or not, the majority still end up in retail. Can you see yourself doing retail? I encourage you to read this:
Job Saturation: Is Pharmacy Worth it? Here's What You Need to Know - The $200 Challenge
The thing is, I'm not sure if pharm school classes are graded similar to med school or more like undergrad. In med school, the best I was able to do in a class was the low 80s (which was also the class average), and that would translate to either a B or B- in the traditional grading scale, which is barely passing if you need a 2.7 GPA.
Again, two different programs with two different goals (grading included for some programs). The school I attended was a 3-year program with a P/F grade, with anything less than a 90% being considered a Fail. As far as syllabus and grading rubrics, it should be straight forward depending on where you wish to apply. I would be more concerned about passing your licensure exam and see what those percentages look like since GPA requirements have slowly but surely not been as competitive as it was 15+ years ago:
North American Pharmacist Licensure Exam Pass Rates
I understand the pivot you now need to do since getting your MD/DO is unfortunately out of grasp at this point, but you still need to ask yourself why pharmacy? I fear you may be running to this out of emotion and time rather than taking a step back and seeing what really might be of more interest to you.
You'll need remediation regardless with other careers, but really step back for a second and ask yourself if you have honestly looked at "all" options. Pharmacy is not in the best position in terms of time, money, commitment, and gratification for many graduates (with plenty of them also doing a career change with minimal to no experience working in a pharmacy). Nonetheless, I do not see you being in a position of not being granted an interview should you cast a wide enough net and still covering your basis of all prerequisites (which I imagine you may have fulfilled in both undergrad and some courses during your beginning semesters of med school).