For the low spots gypcrete should be great, I have only seen it
installed, they mixed it pretty thin, it was completely self-leveling.
I thought about grinding the high spot but I would be careful, it would
be a shame if you hit or exposed one of the pex(?) tubes for the
infloor heating. I would guess that grinding would be a little bit
messy, but probably a lot cheaper if you can get away with it. The only
thing that bugs me is that it may be even thinner than 2" at the high
spot, it would be nice to know the actual depth. If the floor was
already a little high for some reason high they may have only poured an
1-3/4" to cover the pex. If you take a half inch off that it will be
getting pretty thin. I am sure there are guys on the group who have
much more experience than I do with this flooring will have something
Discalimer: I am no infloor heating, or floor leveling expert. But I
will say that the guys who came in to gypcrete a building I did (that
was laid in place pretensioned precast concrete(VERY ROUGH with huge
bulges and dips)) made it look great, very smooth and level.
Oh, and definetly don't jackhammer anything like chickenwing said.