After my local bike shop did a tune-up on my HaiBike Radius, it has become very hard to twist my grip shift into higher gears when I am riding. The grips shift twists easily when I shift down or when the bike is stationary. When I ride, it is so hard to twist that my wrist is sore by the time I get to work. My bike has a Shimano Nexus Inter8 SG-C6001 internally geared hub. I took it back to the bike shop but they said that this is normal because the grip shift is connected to a cable that pulls on a spring. As you shift into higher gears, the spring gets extended and it is harder to twist. I just don't think this is normal since it is noticeably different than before the tune-up. The bike shop said they replaced the gear cable from the grip shift to the hub during the tune-up. The yellow markers are aligned.
Is there anything else that the bike shop could try to reduce some of the force needed to shift into higher gears?
Unfortunately, I do not have the tools etc to complete my own repairs.
Thanks for the help!