99 ZR2 4X4 problem

I’m having problems with my 4x4. When I hit the 4hi it does not engage right away. I have to drive around for a while then if I hit deep snow or an incline and it puts to much strain of the front I hear a pop and it goes into two wheel drive. I stop or drive slow and it goes back into 4hi any ideas?

I’m having problems with my 4x4. When I hit the 4hi it does not engage right away. I have to drive around for a while then if I hit deep snow or an incline and it puts to much strain of the front I hear a pop and it goes into two wheel drive. I stop or drive slow and it goes back into 4hi any ideas?
What transfer case?
Any transfer case codes?
Good vacuum to actuator?
Is actuator locking in good?