I always assumed Slave 1 simply had a cloaking device to
follow behind the Falcon. Out of curiosity
I looked up both S1 versions in the Star
Wars Complete Cross-Sections book just to see what it said. It does not list cloaking device for either
Jango or Boba's Slave 1. However when it
mentions the upgrades for the ship it says, "A
stolen military secret sensor jamming and masking device enables Slave 1 to disappear from most scanning
systems."
The Star Destroyer took off one way and it was Boba alone who
followed after the Falcon. So it would have been Fett who let Vader in on
Solo's finale destination. They both
have working Hyperdives so they both beat the Falcon to Bespin. If you do go with the EU Boba would have known
about Lando and Han's connection. If you
don't go with the EU then I figure the best bounty hunter in the galaxy would at
least research Han's history and again find that connection. I assume without a working hyperdrive Han
would be making a straight line to