98 4.3 4x4, Just replaced the head, intake, gaskets, new plugs at gapped at .60, new cap, rotor, all new fluids, Now my 4 low slips, never did before, put in a new tranny at 120,000 now I have 132,000, I don't do off roading, many used in snow. Vacuum line?? I don't know a lot when it comes to Diffs.... thanks zeb.. Edit: by slipping my mean when I push on the gas it feels like it catches (go's) then it around mid petal It feels like it slipped into neutral, then when I let of the gas it will "catch again" sounds weird I know tranny fluid is fine......

 

If 4hi works, then 4lo should work...

Go into more detail as to what you mean by it "slips"


edit:

How about transfer case fluid?

Does it only do it when you apply large amounts of throttle at once?