The owners mannual does not give me much information/help.

I was discing, 21 ft 1404 Krause.  It is what I had when I bought the 8200.

Anyway. 

The book says to screw the cruise knob all the way to min.  Push the throttle all the way open.  OK.  Now I put it in gear and am running in 9th gear at about 4.2 mph.  I want to go to 4.7 mph.  10th gear gives me 5 mph as it min. speed.  Not the speed I want.  I go back to 9th.  I then have to screw the cruise control knob clockwise to increase rpm to get to 4.7 mph. 

I don't see how this "cruise control" is a benefiting me. 

What am I doing wrong?    or   Is the tractor not working correctly?  Thanks.