Hey up. Using your highlift in the mud shud be fine, providing you are willing to occasionally strip down the axles and pssoibly the transfer case because that hangs so low.
Either run you axles with the diff guards on or use the rubber plugs and make sure all the screws are tight toseal the two plastic sections together.
I run my TLT axles which are basically the same, in some serious mud and when i came to clean the inside i found it was only muddy water and wasnt all that "gritty". I decided it was time to clean them when they started squeeking and creeking.lol.
Mine will be getting some serious mud action!!!!