When my kids were in college, I maintained a fleet of four well used but pretty reliable small 1996 Oldsmobiles for them. I grew pretty good at finding and solving electrical problems with that fleet of four. Initially when there was an electrical problem, I searched for open grounds or broken wires, bad fuses, etc. This was effective and solved most of the problems.
On one car with an apparently unsolvable problem (b.o. radio), I pretty much gave up - but then I removed all of the fuses and replaced them. Problem solved.
So, I have learned to be suspicious of fuses. I recommend that you replace the appropriate fuses even if they check ok. Do the cheap and simple things first. Sounds to me like a blown fuse or two or bad ground has haunted you for quite a while.