I had tried the "terrible T' campaign twice, both times they messed up in early 1944....So I reinstalled RSRDC to do a normal career, started with a Sargo, was upgraded to a Gar, and then a Tambor in early 1943.
I had the Tambor until they mothballed me and the boat in May of 1945. I was getting a Navy Cross with every patrol and had over 300,000 tons sunk, yet never upgraded to a Gato or Balao.
I think there may be a Tambor problem with TMO 2.5