The 386SL adds a cache controller, memory controller, AT bus controller, and EMS 4.0 hardware, which is why it has more than three times the transistors. I checked multiple independent sources before posting, and they all said 855,000 transistors for the 386SL. (Sources from 1990s, so they're not parroting Wikipedia.) The cache controller has a (relatively) huge amount of tag RAM, which accounts for a lot of the additional transistors.