Bassam A Yaseen

Hey every one i have mercedes c300 2015 with 40k on it and i don’t know what’s the problem in gear 1 and 2 and 3 when the car is accelerating the rpm keep rising when it is close to 2000rpm the rpm move back a little bit and my foot is still the same on the gas pedal i put the car in manual mode to know if its the transmission is shifting and slip but even in manual when iam not changing the rpm goes and then it move back a little bit and i fell kind a jerk or loss of power a bit then rpm goes back up normal i took it to my mechanic and he didn’t notice anything wrong help me identifying the problem please it’s irritating 😠 me and it’s noticeable when iam moving slowly or cilmbing a hill