Reg,

Thanks for the tips mate. Im sure if I copy you, which I probably will do, that it will sort the problem, but not really! The gearbox should not be getting that hot running as a stock standard set up. I intend on getting to the source of the problem. I will also do the mods you have suggested as it can only be benifical to the gearbox long term.

I checked my transcooler and its dimensions are 350mm x 350mm, situated directly behind the grill. Not sure if this is standard, or if the standard one is mounted there. The ones on ebay for the F250 seem to be long and skinny. I have room directly below it to fit a long thin one, but not too tall, just behing the number plate. There is 70mm of clearance to fit a cooling fan to the other transcooler behind the grill.