We actually have all the manuals for each year posted on our forum and there is no mentioning that specifically states not to use the 4WD Lock at highway speeds? It's actually smart enough if it's pressed to begin to deactivate above 19mph (30km/h) and is on full auto above 25mph (40km/h), then once you get below 19mph (30km/h) it re-engages the locking system.And it specifically states in the owners manual to not use it at highway speeds.