Look in the glove box at the RPO options. Most good parts stores can tell which brake system you have by teh brake code(should be a JB- or JD- type code).
Yes, that's the label. It appears you have a JC5 brake system which is 4 wheel disc 7200GVWR. From what I could find it says your 4X4 5.3L TAHOE should have dual piston rear calipers and they only take 1 size of rear drum/rotor setup.