I was testing out my 4x4 system today after fixing a vacuum leak and when I went into 4lo and pushed on the gas it was slipping as if the tranny is slipping. But it didn't slip in 4hi or 2hi. Any one have any ideas as to what it could be?
I have a 96 blazer 4 door

 

Something in the transfer case isn't lining up? Could be fluid in the vacuum line that activates the actuator. Are you sure it was slipping in 4 low? I mean that has 2X the torque applied to the tires. Where you going straight & on what kind of surface? Gravel, snow, mud, dry pavement?
What I'm asking is what leads to to think it was slipping, what were the conditions?

 

I was going straight on dry pavement and on gravel

 

Why do you say it was slipping? Were the revs going up but the motion forward wasn't?
Remember, stomping on it in 4 low (which effectively doubles the torque to the wheels <both rear if you're G80 equipped, & front PS - stock open axle) will make the vehicle skip, bounce around & have torque steer.