My 99 4runner rear left brake is locking when I come to a slow stop. Any suggestions on what might be causing it? I tried readjusting the rear wheel cylinders and its didnt help.

Do you mean that the wheel locks up when you apply the brake gently? or that it doesn't release immediately once you take your foot off the pedal?

If the brake sticks when you release the brake, it could be you rear axle seal. Ive had one leak grease into the drum, causing the brake to stick. Very Pricey!