what size speakers are in the back of the 2001 suburban
They're 6.75 inch speakers (same as front), which can be hard to find. If I were you I would go to www.crutchfield.com and select car speakers, then use the car selector tool, they also have good deals. If you replace the speakers, then there is a special wiring harness adapter you will need to use to connect them. (In the rear, there will be a plastic mounting plate that the speaker is glued to SAVE the plate, use it to drill the new speaker holes in). Front is just remove, drill, replace.
Search Chevrolet Suburban Questions
Chevrolet Suburban Experts