Hello, I recently bought a 1999 Ranger 2.5 Manual. It has 178k miles, and a decent number of fixes that are needed.
Bad mpg,
idle revs go up and down slightly (enough to hear, not enough to really worry me),
temp gauge is a tad on the colder side of the middle of the gauge when warm, and the obd reader I have says the ECT is 172-165 while driving.
The brake system has been freaking out a little, abs lights and brake light turning on at the same time after brake get pushed all the way in.
Engine makes a knocking noise intermittently on cold start, haven't really heard it when warmed up, but at the very least it quiets down. Scales with rpms. Not the worst knock I've ever heard, but I just can't pinpoint where it's coming from.
There are other small things that just come with an old truck (this is my first truck, but I've worked on lots of my buddies trucks)

So far I've:
Replaced the coolant with G05, I did a good flush before, although it seems someone did it before I got the truck, because the spigot on the radiator was clogged, so I think they mixed green and gold. The lower hose is definitely free flowing though, dumped coolant all over myself LOL
New tranny fluid as a precaution, oil had been done right before I got the truck, as was the clutch. Tranny fluid was pretty new looking, but better safe than sorry.
I have new vacuum tubes for the vent system, they just need to be installed, it is stuck on defrost currently, the vacuum from the engine was good though.
New thermostat is coming, I think a previous owner put in a 172 thermostat, as it doesn't seem to be stuck open, just opening too early.
New Master cylinder on the way, should hopefully fix the brake light issue.
wires are getting put in as well, I'll wait on spark plugs until the mpg are better, because I believe its running rich in "warm up mode" trying to reach 192, and the thermostat won't let it.
Windshield was cracked in 50 different places, and is leaking onto the mirror, than the floor, so it's getting replaced on Saturday. Oem glass, 385$ plus tax (ouch)
Headliner is drooping something fierce, might just rip it out.

Sorry for the wall of text, if anyone has any tips or must know knowledge about these trucks, please let me know, I'm coming from turn of the century Honda sedans, so a lot of these problems I've never had to deal with.
Thank you!