In the glove box there should be a white label with a list of three-letter codes. My 2001 Tracker RPO code for electric door locks is AU3 and my code for keyless entry is AUO. If you have the AUO code, you can buy key fobs and program them yourself. If all the doors locks are "weak" it's not likely to be the actuators. Are they slow to lock, unlock or both?

 

I'll check the glovebox, that would be great if I just needed to buy/program fobs!

When you hit lock or unlock, you can hear all the locks do a weak "kachunk" and you can see all of the "lock pulls" pop up the tiniest bit, but not enough to actually lock or unlock. The same thing happens when you lock the door with the key, I'm guessing it's supposed to auto lock all the doors when you lock the door with a key? It sounds like it's trying, but doesn't have enough power. Everything else in the truck runs great electronically, it has a new alternator and a new enough battery. So it must be something related only to the locks, just not sure what.

EDIT: We've had the Tracker for around 3 years now and it's been behaving this way the whole time, but it's possible that they failed one at a time for the previous owner(s) and they never replaced them as they failed. It was in our family for about 10 years before that and I don't think they worked at that point either but it wasn't my Tracker at the point so I could be wrong.

 

Study the schematics on this page: Tracker 101: intro to power door locks - Chevrolet Forum - Chevy Enthusiasts Forums
The lock relay would affect all five locks at the same time, but in your case the lock and unlock relays would have to be bad.
Maybe the mechanical linkage is dirty/rusty/binding. May need to pull one door panel and see what's happening inside.
With the door panel off you could jumper 12 volts directly to the lock motor and see what happens.