Fear not J. Francis (what does the J stand for, we're a friendly bunch as you know) you're in the right place here. These trucks aren't anything other than good straightforward engineering, just lots of it in fairly big chunks.
Post up the model number, I expect there's guys on here can tell exactly what your truck has and does from that (but not me). If theres something wrong, it can be fixed. I doubt it is to do with diff locks as you would find it slows greatly on turns on tarmac if the Centre Diff Lock (CDL) is in.
Is this slipping something new or has it come on over time? Some road surfaces can be very slippery when wetted after a long dry spell, especially if the surface is poor. We get it in this country but I've found it much worse in Cyprus where the roads are not to the same standard as here.
Is it wheel spin or skidding under braking or understeer (truck wants to go straight on when you steer) on corners that you are experiencing? How long have you had the truck?
Welcome to the forum even though you've been a member for a while.

Good to have you around.