C172 pilot reported a rough running engine during initial climb and returned to land.

Narrative

This was a maintenance flight for C172S; the plane was having problems with intermittent engine sputtering. The fuel was free of debris or impurities; the fuel lines were flushed; the fuel nozzles were cleaned and the plane was still having the same issues. The fuel servo and fuel flow divider were sent out for overhaul and reinstalled. During runup and ground ops check the engine was running normally. The plane was taken on a test flight; during pattern work of touch and goes the engine was operating normally. A few patterns were done with a rich mixture and a few were done with a lean mixture. There continued to be no issues. I started to depart the airspace to do some nonnormal attitudes to test if that would cause engine sputtering. As I was climbing out from a touch and go at about 6400 ft MSL at cruise power and cruise mixture the engine started to sputter. I immediately started to turn for runway XX at ZZZ and then requested an immediate landing. Since that flight I changed the engine driven fuel pump and did another maintenance flight and can no longer duplicate the engine sputtering.