I got a transmission flush service.

 

Do you think this could be the problem??

 

Tre problems in my mazda started when my mechanic changed the water pump and timing belt 1 month ago. When he was done with those changes, the car was stumbling every time that I speed down the car and he told me that the problem could be the crankshaft position sensor because he got with his scanner a codeshowing him about it. I bought a new crankshaft position sensor and I intalled it, but the problem continues. When I'm driving my car, if I turn on the A/C, the engine stumbles and turns off. Today I just got the code P0750 and I don't know what's going on. I need help please.