I have an old home and none of the floors are level.
In some areas there is a drop of 1 inch from one end of a room to the other end. In other areas where a add on was added the joining slab or seam between the two rooms looks like a speed bump.Wondering if I could cut out these floors at base of wall and just repore floor. It is not possible to use leveler due to amount needed or depth I suspect. Any thoughts other than sell it and start over? LOL

It's always possible to use a leveler, just be flexible on what leveling product you use. Floor levelers are designed to feather out to next to no thickness - but are expensive and not designed for deeper areas. However, thinset makes an excellent leveler at a more reasonable price. While it does not feather out as well as a regular floor leveler, you can fill your deeper depressions with thinset and then add a floor leveler as a top coat.

Any high spots are best ground down first.

Thanks Jaybee! If using thinset 1st what would be the safest maximum depth it could be put down at? Also what would be the recommended prep for the existing slab?

You can do several inches in depth for thinset and still have it cure.

For prep, all you need is a clean and mostly paint or sealant-free slab surface. There are concrete bonding agents that will not hurt but they are not needed for something like thinset or leveling cement as these are designed for better adhesion and can remain stable even if only a fraction of an inch in thickness.