1995 Dodge Ram car traction

Tires and Wheels problem
1995 Dodge Ram 6 cyl Four Wheel Drive Manual

I use my dodge ram, diesel, in a coffee plantation in Honduras, Central America. The roads are on hill sides, dirt roads and steep. On rainy season I have problems driving on slippery roads, the car just won't move on a bit of slippery mud! Eventhougth it is a 4x4! Is it because of the dual rear tires? Toyota's 4x4 pickups do not have problems! Can I take one wheel off the dual rear and use it single like toyota's? Is it because is too heavy up front? Or because of the wheel base being too long? I have tried mud terrain tires, 215/85-16 but is the same. No go! When I got the truck, because of its size I though it was the answer to my hauling problems, I could move more cargo than what I move with my toyotas, but, boy! Was I wrong!
your comments por favor.
Jose R. Flores