The rear brakes have a minimal effect on the braking system. Apply your parking brake while in motion, and see how little it slows you down. It's the front brakes that do most of the work.
How does the pedal feel when you press it? Spongy (think of how a songe feels when you squish it)? Does the brake pedal slowly fall to the floor when applying constant pressure?
The driver's rear caliper can be fixed. The sliders are there to even out the braking force between the front & rear pads. If the sliders aren't moving freely, that's why your rear pad is jammed up against the rear rotor.
The sliders just pop off - the rubber piece covering the slider just pops off the caliper bracket. I cleaned out the channels the sliders go into, and lightly greased them up with bearing grease. They slide easily now with minimal effort. Don't add too much grease, or the sliders won't be able to move freely.
I had a similar problem with my 94 V6 (same brake system on the V6 and GT). I'm not sure exactly what it was, because I did several things at once. Since you've bled the brakes, either your rotors are too thin and need to be replaced, or your front rubber brake lines are worn out and need to be replaced. Thin pads and thin rotors means the caliper has to push farther to apply the brakes; and worn rubber lines will expand and absorb the brake pressure instead of sending it to the caliper.
I solved my brake problem by flushing the fluid, replacing the front brake lines with stainless steel hoses, and replacing all the pads and rotors with new ones. My pedal feel improved dramatically afterwards.