4hi or 4 low? Either way you want to make sure your rolling so that the gears can line up, basically. You can put it into 4hi up to 50 mph, and 4lo basically a crawl, like under 5mph I'm pretty sure. No 4lo on road, and try to only use 4hi when its slick conditions i.e. snow/slush. I'm sure someone can elaborate 10x better than me but thats the basics.
Poverty/College Budget 2004 TJ BB, 1.25" BL, MML, JK shocks, 31x10.5 AT2's
If it can't be fixed with squats or fish oil...your probably gonna die (u aware?)