[Bigdav160]

Officially, GM calls those two digit numbers the "product series based on relative torque capacity". The 4L60e has a maximum engine input torque of 350 ft/lbs. and a maximum gross vehicle weight of 8600 lbs. The 4L80e has an engine torque capacity of 440 ft/lbs and a gross vehicle weight capacity of 16,500 lbs

We were taught in GM school the numbers were torque input values. The 700R4, to differentiate itself from the TH350 used 2 times the torque input because of the multiplication factor of the torque converter.