Gearbox problem
 

So i had a problem with the gearbox for a few month now and i was advised to do a fluid change which i have done reset all adaptions in the box and the drive of the car has improved 100% apart from reverse its fine when it is cold but after I've done approx 30 mile if i try and reverse up a slight incline it will make a huge bang and keeps jumping out of reverse and it wont go backwards at all but will drive forwards no problem at all has anyone had these symptoms before and if so what was the out come i have a 2006 d5 with the tf80sc transmission I'm just a bit worried as i have a 672 mile trip ahead of me in a few weeks i should add it is fine when the car is on the flat it just has me baffled thanks for any info