Our 1996 Geo Tracker has a problem. After a period of driving the car begins to feel like the brakes are on. The pedal is solid at the top of the range and can't be pushed down. The car has to be forced to move. After some time, about ten minutes function returns for a while. Has anyone encountered this?  I checked the wheel temps and found one front about 30f hotter than the other so I freed up the stiff caliper but the same thing still happened.
 Possible contributors
 Towed a thousand miles + with a brake buddy doing the stopping. I understand that these can exert a lot of force.
 We had to add a lot of fluid once but it stopped leaking. I could find no drips. Might be master cylinder or unrelated.
Any and all help will be appreciared

You say you found a temp increase on one caliper? Have the front brake hoses ever been replaced? It's common for them to swell inside & restrict fluid return, even if the look okay outside. By your description that's what I would suspect.

If your caliper is stiff I would probably replace both of the front calipers at the same time as replacing the brake lines.  Small insurance and it's pretty annoying to have to replace the caliper in a parking lot.