IDK about diesels but it sounds to me like yours is either working too hard or not up to the task. The GV unit has a .78 split. meaning that if you shift at 3000, the Rs will fall to .78 of that or to 2340rpm, on the upshift or 2340 will rise to 3000 on the backshift........ but you cannot outshift the GV under power. So if climbing a hill, in say 3rd/over, and you wanted to go to 3rd, you would have to figure out a way to disconnect the engine momentarily to outshift the GV.
I'm thinking that will not be very useful to you.
Better I think is to just stay in whatever gear it takes to climb your grade
