Hmmmmmm
Could be many things
A couple of thoughts
As you say it only happens when you have full weight on the wheels
Drop your diff oil, pull off the cover and have a look, check the oil for metal and the condition of the drive pinion, ring gear, side gear etc
Idealy you should do both wheel bearings not just one, check them again and make sure they are installed correctly and have plenty of grease, check the rear pinion bearing, if the bearings have not had grease pushed into them by hand before installation they can dry out, check your calipers are secure
Check your drive shaft both ends, yolk and uni, check the tension on the bolts @ R2oo diff 49 - 59 NM R180 diff 31 - 42 NM
See how you go
Cheers