The phrase "drove back forth" can be replaced with several synonyms, depending on the context of the sentence. For instance, if you're describing a ship or boat rocking back and forth on the waves, you might use "pitched and rolled." If you're talking about a car or vehicle driving repeatedly on a stretch of road, "shuttled" or "shuttled back and forth" might be appropriate. Other possible synonyms include "oscillated," "fluctuated," "swung," or "alternated." Ultimately, the best synonym depends on the context and the connotations you want to convey, whether it's a sense of regular motion or something more chaotic or unpredictable.