Maybe you're asking what's the max speed you can drive in with 4WD engaged.... that's one I've always wondered. I've taken the Detroit freeways at about 50mph sometimes and it sounds like my VX is going to blow up even though it's at about 4000 rpm I think. All the gears are just screaming. I know it sounds like you wouldn't want to go that fast if the road was slippery enough to have to use 4WD but here it's the choice between going 15mph in the slow lanes or 50mph in the GrandCherokee lane sometimes. It'd be the perfect time to have a switch that would lock it into 4WD-high.