Mercedes Benz Engine Stalls when put in Drive Mode

2008 Mercedes Benz R350. Changed the cv axle three months back with an
indy shop. After changing the axle what I am noticing is when I am on a uphill
(even a small angle of 15% upwards), and when I engage the gear to drive
mode and press gas pedal the car behaves liek I am applying break.

Strange symptom. It does not occur every time but is happening more now.
Ex below,

1. Car parked in drive way which is slight uphill of an angle of 15% or less. I
start the car, engage the gear to drive and press the gas pedal. the car
behaves like I applied  the breaks. Then it starts  to move on. I hear a hissing
sound inside the car near the drives seat.

2. I am driving the car and everything is normal. I come to a stop on a small
uphill for a stop sign. I stop the car by applying break. Now I am already in
drive mode and when I press on gas pedal the car is like again applying
breaks.

No check engine light have come anytime. Can anyone please throw any
light. Is this related to recent cv axle change or completely unrelated.