Replace lost coolent after pump replacment?
Thermostat installed upside down?
an old hose could partially collapse after pump change due to cavitation- check all hoses while ideling hot-
Could be a bum stat-
wide temp changes usally indicat a low coolent level, faulty stat, air in system, worst case head gaskets, ect.... Sometimes something as simple as the radiater cap not letting off pressure can affect boiling points and cause problems.
I have seen undiluted antifreeze cause problems, but not normally... hope this helps....