Car shudders between 18 mph and 50 mph

[IF83WRC]

Hello
I have a EDGE ST line-  2L Ecoboost 238 bhp, powershift 9000 miles, bought this year . That's the short presentation of my car. Now the problem...When driving on long rides ( more than 100 miles ) and especially when climbing, the car shudders between 18 mph and 50 mph.... After 50mph the car runs just perfect . I went with the car at a Ford dealer and explained the problem... They told me that's impossible to discuss about a mechanical problem to my car and it seems to be a gearbox issue..So they installed a new update to the gear box. Few day ago, I went on a long ride and the problem occurs again...What's frustrating is that there is no error stock on the ECU, and the problem appears only between 18mph and 50 mph after some miles . This friday I'll get the car to Ford again, but how could they identify the problem if the problem occurs only in some conditions? Any ideas about what to suggest them to look for? Cheers !