With that description...if it looks like I expect...you probably need to rip out and replace. Part of your issues will be age and inadequate reinforcement and/or depth but I would bet a c-note it is mostly improper prep with a dash of drainage issue if your soil is even slightly expansive (usually clay).
So if you want to verify, drill some test holes with a hammer drill. Check concrete depth (probably rat-slab 2-3"). Then stick a piece of rigid tube in and pull out a 3" deep sample. It will be dirt and likely either lots of organic material in it (settling) or clay (jacking).
If I am right, you want a pro or gifted amateur to assess what you need. With organic, uncompacted soil you usually scrape off 6", put in compacted gravel. For clay..it gets more critical to avoid drainage issues from the garage and for about 10' feet minimum around it...then do a decoupling membrane and sand.
All that said...want a redneck fix? Knock out the high spots and re-pour those. Drop in 6 x 6 mesh and poor a 3" rat slab right on top. Bonus if you rent a concrete nailer (Ramset, Hilti, etc) that can shoot either studs or forming nails in the existing slab, tie the 6 x 6 to that elevated at least a 3/4" off the old slab.