Hi,
Your not alone, same thing for me only 5th-6th, stored away over winter, had a service early this year and my gearbox feels well different when under power from last year, it has got better, I tightened my chain and lowered the lever a little bit.
Yours should ease up too after a few miles, can't imagine why it would do this, not a great start to my biking season.
Good luck.
