I REPLACED REAR BRAKE PADS ON MY 99 CHEVY S-10, SEEMED FINE BUT THE NEXT DAY LEFT/REAR BRAKE LOCKING UP, HELP PLEASE.

You sound competent enough to figure this out.

I am with u on this. the light should be on. my advise is to check with someone else. also why not get the part from junk yard

Could be your emergency brake cable is locking up,could be just one side on the rear.

Have you changed the brake hoses on the front going to the brake caliper?If not,this could be the problem,also,when bleeding,only pump the pedal one time upon releasing the bleeder screw,do not pump the pedal,start at the master cylinder,then the right rear,and the left rear,and the right front and left front in that order,adjust the rear brakes to where the brakes are dragging pretty good,but are not locking up,

Try having the dealer flush and bleed your system. It is very hard to bleed ABS systems yourself and have safe brakes that still work afterward. Bleeding non-ABS brakes yourself is easy not the same for ABS brakes. Valving, sensors and what-not require a tech and the correct equipment in my opinion. You do it wrong and you could ruin your ABS system. Do that and see if they firm up. I replaced my brake shoes/pads at the same time all new everything in back, drums/springs everything and new rotors up front. then I had the chevy dealer flush, refill and bleed system. Stiffer pedal and brakes work better. Keep in mind the brakes on 99 Tahoes are inaedequate, require new rotors often, heat up and fade/glaze pads regularly. I replace my pads long before they wear down because they glaze up and start fading early. I'll rough em up once maybe, next time, new ones. Every two brake jobs, new rotors for me. Just how it is. They will stiffen a bit and work better but they will never be awesome brakes. Just how it is on 99 and earlier Tahoes. Hope it helps. Very important to bleed correctly though. I'll bleed my 83 Toyota 4x4 myself but not the Tahoe.

I would replace the rubber brake hoses at the calipers. They get damaged internally when the calipers are left hanging while replacing pads. I've seen too many garages and shops do it not knowing what is going on inside the hose.

you still have alot of air in the lines.or you got a bad caliper

You say they replaced basicly everything that involes the rear brakes.
Every step they took to find the problem could lead to the solution,BUT did they check the inboard brakes. The brake system on a jeep that has rear rotors have inboard shoes for the parking brake.
You could have a parking brake cable that is frozen (this will cause a drag on the inboard brakes. Do you use the parking brake? Maybe the parking brake shoes are adjusted too tight?

todays sports utility vehicles are equiped with a proportioning valve. they are usualy located at the rear of the vehicle. this valve regulates the flow of brake fluid to the calipers. most suv`s have a ride control arm on them that is linked to the rear suspension to apply more braking force to the rear wheels in a harsh or sudden stop. if this valve is bad or malfunctioning even body roll can redirect brake fluid to the rear wheels causing them to lock up., hope this info helps

you have either calipers hanging up or the lines are separated on the inside causing the fluid to not be released back after application of the brakes.. to test... remove the caliper on the pass side first (farther from master cylinder) and slowly try to push the piston in using a c-clamp.. if it doesnt go in SMOOTH then crack the bleeder screw, and try again, if it goes in just fine its the line.. if it goes in the first time fine then go to the other side and try it. if one of them DOESNT go in fine with the bleeder broke open you need calipers (very common) and then you will need to bleed the brakes and make sure to start on the side farthest from the master cylinder i.e pass side