I think somebody above mentioned check the temperature at each wheel when you stop after a trip. I have a cheap IR gun that I have used to track down caliper pins that I did not sufficiently grease. In my case I played one of these is not like the other.

Are you getting a firm pedal when you bleed the system after you do the pads? And how crusty are the slide pin channels in the caliper? Dried up grease solidifies in there and, over time, gets shoved to the back of that recess. The result is that the caliper pin doesn't go all the way in and also does not sit parallel to the slot and mahender proper movement of the sliding portion of the caliper.

I should clarify that the junk gets built up in the rubber inserts for those channels and that they can be replaced.. if they tear while on the vehicle then you get crude in behind them and that's no fun. I would suggest changing those rubber boots for the slide pins
There is a neat trick to reinserting the replacements since they are actually a slightly larger OD. It involves tying a string around the base. It's out there on YouTube. Seems like you're going to tear it but make sure the channel is appropriately lubed and you should be fine. Order a couple textures just to be safe. You will be surprised how scuzzy the insides of the ones on the car actually are.

 

Temp check results???
Brake line implosin, replace all brake hoses AND rear wheel cylinders.cheap on Rock auto Dude!!
Suspect rear drums not doing their job, nobody really does drums thoroughly any more