Found the problem, another caliper, rear passenger, was frozen plus the clip that held the ebrake shoe in place broke off due to rust so it was leaning into the rotor wall scraping, and the inside pad was also worn down metal to metal with the inside part of the rotor pretty worn thin as well. What a mess and neglect by my bro-in-law, that truck deserves better for what he paid for back in 02 (listed at $38K). Replaced the whole caliper plus the bracket, as it only costs $8 more with the bracket, also a new rotor and pads and bought the ebrake hardware clip while retaining the old shoe. Taking the bolts off for the bracket was a b---ch, but after some pounding on the wrench and PB blast I broke them loose. So while I was at it, I was a glutton for punishment and checked the driver side rear brake assembly (the fronts were already worked on), and I had to use the new set of pads anyways since they come in pairs. Also took off the bracket on that side but did not replace, only the pads, as there were no signs of rubbing, but based on the pad wear it looks like that driver's side rear caliper will need replacing soon as well. Those pads were a pain to put on too, I would have grinded the tips down a little if I had the patience but just pounded them in after lubricating the sliders that they're supposed to pop into.
The dust shield on both side are also gone due to rust, just broke them away, and I'm looking for some replacement shields that can hopefully snap-on instead of having to bolt on. Cleaned up everything, also rust-treated the old bracket I didn't replace but put brand new bracket bolts I happened to have on-hand as spares when doing the fronts, so it won't be a pain to take off once I have the money to change that caliper. Looks and sounds good so far, nice to be pulling up in the parking lot at work without everyone staring at you for an annoying scraping metallic sound. At least progress was made again.