Toyota Repair: Camry 2007 transmission problem, mile powertrain warranty, oil spillage

Question
I have problems with the transmission of my Camry 2007 XLE V6 with 45k mileage , it cant seem to change to a higher gear whenever i try to accelerate, it just revs high, cant change from gear 3 and above. at some point when it began, i usually see smoke from the engine as a result of transmission oil spillage and i haven't been able to locate where this spillage is from. I took it to my mechanic and he drained the oil and replaced it with fresh oil and no changes still, he has ran it through a scan and discovered no fault, he also brought out the filter in the gear box and cleaned it up but no improvement.
He is now advising that we change the Brain box of the vehicle.
can this by any means be the solution? or do u have any other solutions to this problem?

pls help

Answer
There are several known issues with the 2007 camry transmissions and toyota has some service bulletins that may apply to this problem, I would advise you to go to the toyota dealer and have them check this, the ECM may need to be calibrated, even if it has to be replaced the warranty is for 8yrs/80,000 miles, if it only needs to be calibrated then it's also covered under warranty, even if the entire transmission has to be replaced it's covered under the 5yr/60,000 mile powertrain warranty.