Ok this might come off as a stupid question, but can someone please explain to me the structual difference between a T45 & a T56. Heck to me it looks the same, but mind you I am a girl and wouldn't know anything about cars ....besides the fact that they are only in a 4th gen F-body and the 56 in supras and vettes. But anyways... please enlighten me.

 

The T56 is in the 4th gen. Also Vipers and CTS-V's

 

The T45 is a borgwarner designed transmission for the late 90s mustangs. It was a similar design to the T5 but a bit stronger, in other words old technology with some minor upgrades. With transmissions it comes down to size of gears,shafts, and shifter parts. The smaller the gear, the less area to spread the forces out and the weaker it is. Same goes for the shafts and shift forks. The T45 has smaller gears than the T56 and that is why the T56 is stronger. It was replaced very quickly in the mustangs by a tremec tranny (which has weak shift forks but stronger gears )
Tremec has taken over a couple smaller gear companies (including borg warner) and it looks like all the new R&D they gained is going to good use. They are starting to build some solid stuff.