rear diff

i have a gmc sonoma with 3.73gears and posi with 4wheel drive when i go to pull out in wet grass or mud in 2wheel and i start to spin my rear diff slams between both wheels very hard i no posi will go back and forth but mine is very hard and you can hear it clanking

Pull the inspection plate and have a look in there.
Look at the flipper setup on anti lock
Also look at spider gears and pin.
MT

i had the cover off the spiders looked ok there was some metel on the mag not a lot but some what am i looking for when you say pin and the flipper also it has rear disk brakes i used 75/90 Rp max gear whene i changed the fluid it did before i changed it also

Give the drive shaft some quick spins and see if the anti lock flipper locks in both rear axles.

it is just locking one side or the other with it in the air and in drive ideling it switches back and forth about every 8sec between each wheel whene it does this it is harsh but if i turn the drive shaft fast it just spins one wheel or the other

Hanging in the air at idle is not the proper way to check.
Hold on wheel and give A quick spin by hand on the drive shaft.
Both wheels should lock in and both turn .
If not the anti spin device is not working right.
A good factory repair manual or some good repair info would be a help to show you how it works and or how to fix it.
MT