ZF5HP24 Gearbox slamming first gear with no obvious signs of malfunction.

Hey Scotty,

I was wondering if you had any idea on what else could be causing a gearbox problem on my Jaguar XJ. Its a ZF5HP24 and has been slamming itself into first gear when moving anything lower or stationary than 5mph. It is as if it is slow to start engaging and then just slams it in once the RPM's have risen as the car does start to creep forward when you lift off the breaks, there is no grinding as it does this it just lurches the car violently forwards. It was leaking ATF from the sump and after researching, low fluid was the common cause of these symptoms so today I did a filter and fluid change with a new gasket, the old fluid was very clean with no signs of being burnt the filter was not clogged and the magnets wernt covered in metal shavings, so on face of it looked like it was the cause, however, it is still slamming 1st gear in the exact same way as before even tho its full to the correct level with new ATF. Is there anything else I can look for as there are no codes and no other obvious signs of malfunctions and a replacement is rather expensive?

Many Thanks