Need help with hubs!

[brown78]

I am having a problem getting my hubs to engage. 1971 Chevy blazer, Warn manual hubs. First i tried to take them apart, clean, inspect, reassemble. On jack stands they would engage, on the trail not so much. Bought a brand new set of Superwinch quarter turns, installed, same result. I noticed if I drive 20mph or so down the road they seam to engage, slow down put a load while trying to climb a hill, nothing. Drive down the road at speed, slow down, put it in 4lo, cut the wheel hard and slowly turn and the wheels chirp, hubs engaged. Go into the mud, turn and gas it, only rears are spinning. Now i'm stumped and aggravated, time to walk away and ask for suggestions.