I have a 2000 Expy with 4AWD, 4H and 4L that i just got. When i first got it, it seemed to like shudder or grind or something. it did have 1 different sized tire than all the rest. I got new coopers and that seemed to fix that. It snowed today and when i would start driving from a complete stop or when accelerating on a slick surface, there seemed to be a jump or jerk from the wheels. this would happen in 4awd only but not in 4x4. How can this be fixed?

 

Prolly nothing wrong.
When in A4WD, and the rear wheels turn faster than the front wheels, the electromagnetic clutch in the transfer case is pulsed to begin locking the front and rear driveshafts together which (automatically) engages four wheel drive. It can engage suddenly and that is prolly what you feel/hear.

 

That's working as designed, it's not a 4AWD system it's a A4WD system. You're thinking of an all wheel drive where there's some sort of constant power to all of the wheels. With the Ford A4WD it's an Automatic 4WD. In other words power only goes to the rear wheels until slip is detected then power is applied to the front wheels, hence the sudden grab.