Yamaha 300 XCA Help

I have a 2018 300 XCA on a 2018 Sportsman 241. During break in I could get 48.9 MPH at 13 hours. At 22 Hours, I could get 50-51 MPH at 5580 RPM. Took it in for service at 33 hours. Since I haven’t been able to get over 40 MPH and cannot get over 5450 RPM. Took it back and they couldn’t find anything wrong. Said they had it to 5800 RPM but didn’t check the speed. I can get it to 5800 RPM but have to trim the motor so high I lose speed. My throttle has no response past about 3/4 to full throttle. Has anyone seen this or have a possible fix? Thanks.