4x4 high and low
 

I know this sounds stupid but is there any speed restrictions on 4x4 high? I plan on using this to drive on the highway this winter. I figure 4x4 low is just for really slow speeds.

Not really provided conditions warrant using 4wd. The drivetrain can bind up when turning even just a bit in 4HI on clear roads. Overtime, it will cause wear & tear on the parts.