The TH350 came with a 2.52 low gear ratio from GM stock, period.
The Th400 came with a 2.48 low gear ratio from GM stock, period.
There were never any other gear ratios offerred from GM. I rebuild these units and have multiple references to this including GM service manuals, ATSG tech manuals, as well as other reliable information, not including the hundreds of each unit I have personally rebuilt. There are several other very knowledgable transmission guys who frequent here who can confirm this.
There are aftermarket gearsets available for both the Th350 and TH400 to achieve a 2.75 ratio low gear. This requires a different pinion gear tooth count as well as a different sun gear tooth count.
The 700-R4 came with a 3.06 ratio first gear, some call it a 3.07 ratio. Again not the Th350 or 400.