Ford s max 2.0 diesel auto 09 plate

Hello to anyone reading this and thanks in advance of you can offer any information I have read a lot of threads on here with very similar issues but never seen a definitive answer.  I have a issue I drive 30-40 nice slow seem to get a bit of a judder sort of feels like a fuel related issue then accelerate quickly as in drop my foot and keep a constant increase then esp light comes on and service transmission required the gearbox seems to go into limp mode if I push it over to s mode it will not let me change gear just stuck in whatever gear it’s in I’m fairly sure it’s not a gearbox problem as if I drive slow and steady no problem even if I drive 50-60-70-80 on motorway but very slowly increase to this speed it drives for as long as I want it to without any issues but if I’m driving at 50 and go to overtake and start to want to increase speed quickly ot just comes up with esp transmission etc goes to limp mode  gone to a trusted long life friend at his garage we was thinking can problems used for scan and a number of issues but none definitive he uses his snap on diagnostic and same a few issues we changed map sensor, mass airflow,full service all filters etc , actuator sensor (the one at the bottom of the actuator) , turbo boost sensor,re mapped the ecu to rule out a dodgy pre map  checked all viable ground lines replaced the steering angle sensor (new from Ford) had a egr, flaps delete and blank it off and we have a red issue on the turbo side of it any help appreciated I don’t know what to do next as a turbo is costly and also possibly not the problem