auto box not locking properly

hi folks , i have a wierd problem with my d2 td5 auto and was woundering if any of you knolageable lot have any ideas ??
ok here we go, the auto box drives fine except that when you expect the torque converter to lock it sort of half locks , if you take your foot off the gas it is locked enough to keep the engine revs up but not to transmit any power !! so now you are all thinking " easy the converter is chuffed" BUT !!!!!
if i put my caravan on the back it locks and locks solid , no slip, and at the correct speed ......
i have bought a nanocom and pluged it in to find p1884 can message md_ind invalid [ flag f_tl_mes]
this seems to be a universal can bus fault but if anyone has any other ideas all are welcome

to date i have done the following , gearbox valve chest strip and clean , mv 3 replaced , maf sensor replaced, oil and filter changed,
today will be a strip and clean of the xyz switch as ive had the air con on ,
i am sure this is engine torque related , could it be the engine ecu??? it has a dynachip remap and surface mount chip
thinking caps on please gents thanks










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