Well if you absolutely have to activate truth before startGathering() you can use sendIcon() function. For example to click on hotbar 7 slot 3 and wait 1.0 second do this:
sendIcon(7, 3, 1.0)
Or you can make a macro in the game instead. For example if your miner set is #20:
/macroicon 20 gearset
/gs change 20 <wait.1>
/ac "Truth of Mountains" <wait.2>
Put this macro on hotbar and Miqo will see it as common gearset.