S8 D2 erratic gearbox

[Snaggle57]

hi everyone, have a few issues with my gearbox im trying to figure out

i have searched and searched for an answer so apologies if this has been covered before

the only similar thing i found was a thread by hpsauce who said he sold the car before rectifying the issue (thanks for the reply)

i've got a 97 S8, AHC engine, DYM gearbox, TCU code ends in BG

had it a couple of years but its started misbehaving, its not all the time and there seems no rhyme or reason to it, its just bloody annoying

if i got into a tight corner, when i try to accelerate away the car shudders for a couple of secs, as if a clutch is slipping, because its in 3rd and should be in 2nd, jab the throttle or wait for the shudder to end and it then drops into 2nd and away you go.

and then sometimes when i slow down in a straight line the gear change is erratic, usually 4-3rd or 3-2nd, the change down feels like i have jabbed the brakes for a split second

these things dont happen all the time so cant work out if the gearbox is goosed or the gearbox tcu could be the culprit?

the car throws up no fault codes and ive checked quite a few times

in tiptronic mode the car drives spot on, no slippage or erratic changing
kick the arse off it in auto and it drives fine, but i cant be doing that all the time i'll end up in a ditch!

if anyone else has had this problem please let me know, in my mind its terminal gearbox so anything other than that would be a bonus

thanks in advance!