4 Wheel drive problems- 1993 GMC Sierra 6.5 Turbo Diesel 1 ton. (Crew cab-dually)?

[thetalisman]

When 4 wheel drive is engaged, there is a consistent surging (surge-surge-surge-surge), especially when going up a hill or accelerating. Also if I'm in an area that is not as slick with snow/ice (I'm getting a little more traction), the truck is becomes almost uncontrollable. It fights me to the left and if I correct with a little force to the right- the truck suddenly wants to veer to the right....and visa-verse. It's a constant battle and quite scary, but when I'm not in 4 wheel drive, I don't have these problems. Any insight?

 

[Sam Chicklets]

Are all the tires the same make, model, size and wear? If you have different tires side to side or front to rear this will cause these issues.