Wacky action on '01 Fender MIM Bass

Hi,

I've always stalked these forums but never posted anything, so this is my first post. I taught myself how to play bass years ago by reading all over this place and I found talkbass to be a great resource, and I check here first for anything bass. I was wondering if anyone could help me out. I tried searching my question in different places but I wasn't able to find anyone with the exact problem I'm having.

I have an old beater 2001 MIM Fender P Bass. Although I have other and better MIA basses I could play, I've been wanting to revive it and make it more playable. I recently changed the pickups to the Fender Original '62, gave the entire body a shine/polish and next on the list was adjusting the action. I don't play this bass that much and it had extremely low action which resulted in pretty short sustain. I do like my action a little on the lower side, but that was just too low. I couldn't remember the last time I adjusted the action on this bass.

I spent hours trying to get the strings to a decent height that felt consistent across the neck. I really could not settle, nothing felt right. I tried making it a bit higher, and though it helped a bit, the action was too high (much higher than any of my MIAs, though I do understand they have much better QC). At about the 3rd fret, up to the 11th, there's a good amount of fret buzz on the A string. If I play the 12th and above it's mostly gone. I have similar issues on the other strings, random pockets of fret buzz (between the 2nd and 7th on the D string for example). I'd think if it was a truss adjustment issue there'd be a pattern, like they'd all buzz around the nut or past the 12th fret.

I was thinking maybe something's wrong with the neck, since I do take it outdoors often in the summer/winter, switching between warm/cold fast. It doesn't have a case either, just lays around, thought maybe buying a new neck would do it but it's a bit costly for a bass like this. I've read up a bit and began thinking maybe it just needs some fret leveling. That could make sense to me since it's nearly 20 years old, I bought it used around 7 years ago, and looking at it, it has taken a bit of a beating over its lifetime. I've never done it myself nor heard of it before this, but I wouldn't mind the risk of screwing up the frets if it means I learn something. I'm just not sure what else I haven't tried yet.

Basically: weird action on the neck, buzzes in different places on different strings, truss rod adjustment doesn't fix it for me, maybe needs fret leveling?

Any comments/suggestions would be helpful. I can provide clarification if needed. Thank you!
 
Do you have any measurements for us? Relief, string height, etc.?

What type of strings and how old are they?

Elixir Strings 14052 (0.45-.100). They still have plenty of life in them, changed several months back. I usually change Elixir's once a year.

Relief is roughly 0.14in.
Low side string height about 7/64, high side about 6/64.

Hope that helps.