Clunking noise from the tran

Last week I went to put a few more hours on my new Grizzly. I have almost 6 hours now on it. :icon_ nono2:
I know what you guys thinking, however time is still a luxury for me and I don’t have a lot to spare.
Looking forward for my trip in September. I will have a week to go and ride the quad. I want to be done with the break in period by then, do my oil change and first maintenance and be ready.
I need some direction or feedback on how to ride when to use low gear and when can I use high gear.
I’m listening to the engine and is spurring nicely . the terrain i’m riding is mostly hills, quite steep hills, and I’m questioning if I should ride there considering my engine is still breaking in. Sometimes I have to push the accel more then half to keep the engine running and not bog down. During engine break in period is that Ok?

Question for you:
1. I was coming downhill in High gear 2X4.
The engine had still a lot of braking and the speed I was going was comfortable enough for me to control the machine without using much the hand brakes.
At one point the speed increased a little and I heard some clunking noise in the trans, coming from my right foot area.
It clunk once or twice and as soon I push the brake and reduced the speed it went away.

later on I was in the same situation and I heard the noise again. .
I switched to low gear and 4X4 and everything was OK.
In 4X4 the quad is barely moving downhill. I have to push gas a little to keep it moving.
The engine break is phenomenal.

From your experience this noise was normal or is something unusual going on?
I also sometime have a very hard time switching the gears.
I feel the rod bending under the pressure but it will not disengage or get into the next gear.
Is this something I have to be worried or is normal for a new machine?