wheels skiding when in 4wd

hi iv just developed a fault when in 4wd the wheels skid on and off and feels like your driving with the hand brake on but fine when in 2wd, also the hubs dont unlock after selecting 2wd and driving forward i have to reverse a few feet then i can hear them click and unlock! it happens in gear when driving also when in nuetral rolling down a steep hill.
it started after getting stuck on wet mud and grass, i was revving high in low ratio with wheels pointing front and on full lock
also miby worth mentioning i have recently replaced the rear axle but feels fine in 2wd.
im thinking auto hubs or transfer box?

any sugestions would be great!

what wheels are skiding front or rear

I'm thinking you have the wrong rear diff if that was also replaced.

was all but rear wheels now?

the axle was off a 2005 model mine is a 2000 are the diffs different?

id go with the wrong diff

jack up the front one side and the rear as well then start it up put it in 4wd remove and brake make a mark on the side wall of the front and rear wheels that have been jacked up then turn the rear wheel 3 full rotations and see if the front wheel has turned the same and the mark is in the same place