Nylock nuts are a one time use item, once the nylon insert has thread grooves it no longer has suitable holding properties when a bolt or screw is threaded in the next time.
A cheap way to make nylock nuts is to take a regular nut and place a zip tie through the center, then thread the bolt/screw in, instant nylock!
If nylock nuts arent available thread locker can be substituted.
Try Home Depot for new nyloc nuts, look for stainless steel hardware since its going under the truck.
For your squeek try this:
lfit the back of the truck by the frame and allow the leaf springs to fan out, hose them out real good with a garden house, make sure you wash all the dirt, grit, and dust out. Lower the truck and drive around to see if this doesnt get rid of the squeek.
Tips to prevent spring squeeks:
Never use any typ lubricant on springs and or bushings, lubricant attracts dirt, dust, and grit causing squeeks between the springs and in the rubber or poly bushings.
Take apart the spring pack and place squares of tephlon between each spring as you reassemble, this allows movement on the tephlon but not metal on metal which causes squeeks. Again never oil!!
