Been around trucks for as long as I can remember. My father was a t&t mechanic for most of his life. I learned how to drive a ten wheeler before a car. I did some long haul, then got into construction, then became a grader operator. I still drive truck now and then, ten wheeler, dump trailer, or moving equipment. Boss loves that I can float the grader to and from Saturday jobs myself without having to call someone in. I've run most transmissions. Most of the company tandems have 8LLs and the tractors have 18s. I ran a lot of 13 direct, and 13 overs when I first started driving. I run an 18 like a 13 and mostly split the high side gears. Is there ever really a reason to split the lower gears, or is that more of an off road, hilly country thing?
Don’t split unless you have to, i.e. heavily loaded, mountains, off-road and taking off on slippery situations. Don’t lug/load the engine as you know what that sounds like and your crank bearings will thank you.