Yes sounds like idling too high, try 7-900 I run mine low.
If the idle is high and engaging the belt, then yes the springs will do that though not necessarily too tight. With the springs installed there is always engagement forward in forward or brakes in reverse, a high idle will basically give you cruise control effect with springs attached.
Figure that out first, then the top end thing. You didn't mention what size tires you have, a Max IV with 21's is not that ( 25mph) fast.
My new beer holder spilled some on the trails - in it's hair and down it's throat.
Joe Camel never does that.
Advice is free, it's the application that costs.