Problem with Nissan Pathfinder 05

ok, heres my problem...i bought an automatic 05 nissan pathfinder in oct of 2009 from a dealership. They gave me 6 months warranty on the engine and gearbox. almost as soon as i got it, i was noticing some irregularities with the transmission. gear-changes were occasionally rough, and when stopping at traffic light for example, it would cut out, or when accelerating again would be extremely sluggish. to resolve this i would usually have to switch the engine off and restart it... which worked everytime.

i was prompt in taking it back to the dealer and explaining what the problem was. he explained he wasnt sure but would sort it. within the 6 months of the warranty...i went back 3 times with the problem and on the last time he said he would change the gear-oil and hoped that would sort it....IT DIDNT. so in Dec 2010 the gearbox seem to fail...there was no drive to the engine...i had it toed to the dealership where i bought it. He checked it out and said after looking at it that he 'wasnt an expert' on automatic gearboxes and it would have to be sent to a specialist. I got a call from the automatic transmission mechanic a few days later to say that the radiator has leaked and spilt into the gearbox...'major job'

So just looking to see if anyone has had a similar problem, or has any advice. The fact that i was within warranty when i took it back to the dealership. Also the fact that if the dealership mechanic wasnt an expert in automatic gearboxes....why hadnt he sent it to the specialist when i first started having trouble with it.

Any help would be much appreciated!!