Whether US forces were driven from a beachhead depends on the definition

Was Dieppe the only time US ground forces were driven from a beachhead?

Probably only under a narrow technical definition; actions in Canada during the War of 1812 may provide earlier examples.

Fighting in Canada during the War of 1812 may provide earlier examples of American ground forces losing a beachhead. Whether those cases count depends on the definition of a beachhead and the forces involved. No specific engagement is identified, so Dieppe's claim to uniqueness remains qualified.