Fleet auxiliaries reveal operational intentions

Would greater U.S. investment in fast oilers have changed the Pacific campaign?

Probably; fast oilers and amphibious ships set the pace of operations, and their movements could also reveal Allied intentions.

Fuel and landing ships set the pace of operations in the Pacific war. Combat formations cannot move beyond the range and capacity of their oilers, while amphibious shipping limits where troops and supplies can be put ashore. Scarcity in either type governs operational tempo even when the fleet has enough combat ships. An intelligence service watching those auxiliaries can infer likely Allied objectives before the fighting begins.