Transmission or electrics? HELP!

[L6eux]

Hi Guys. Recently purchased my first Lexus RX300 2003 new shape, The first few weeks I had no problems. Then one night it rained and the sunroof leaked badly. Inch of water in the footwells and the water had run down the pillars into the dash. I then sealed up the sunroof and dried out the car. It seemd fine to start with but then as I was driving it started acting a bit weird. It would kick down and up gears for no apperentt reason. The fault doesnt happen all the time its now an then. Ive had it a friends garage and he says the gear box is faulty and needs replacing, but having spoke to another mechanic he says the electrics may be damaged and cause the ecu to get confused thus changing gear when its not supposed to.  Any advice or Knowledge would be great,

[PCM]

Sounds like the electrics got water damaged or there's still water/damp present?

Did you clear the sunroof drain holes?

Is the car dry now inside?