loose nut in my rearend

If you are talking about the yoke nut you only get one shot torquing it properly to get the compression seal to work. There is some reason it backed off. It was either not torqued right in the first place or like ruthless said you have a yoke bearing problem. They wouldn't know that unless they disassembled the whole thing. Not only use a new locknut I would use thread lok on it. Keep an eye on that seal for a leak.

How many miles on this truck?

It reminds me of a joke but we won't go there. You just giggle to yourself. That's why they call you Giggles!

 

Like was stated if the yoke is tight on the splines, You need a puller to get it off, you can just tighten it using a new nut with Blue Loctite, is great, if the yoke is worn or the splines it will loosen off again. You do want to keep looking at it. Spray some paint on it then if it backs off you will be able to see it.
If the nut has a nylon insert then it is reusable if the threads are OK just take a hammer and with the nut on a flat surface hit it in three places with a hammer. Alison alows the nut to be used up to 10 times.
The steel crimped nuts must have a lube for the crimp to stay usable. I use to use Never Seize, mixed with synthetic gear oil and ATF. Blue loctite is OK also.

 

I had this bout a year ago yoke was loose tighten up couple weeks later same thing noticed a lot more threads when tightened second time ,this was a Rockwell axle , pulled out threw shaft 4 allen head bolts on rear ended up shaft where the bearings go on the shoulder broke off where bearing rides and let the shaft pull out further than it should have bout a half inch back when yoke nut was retightened caught it before it tore it up just a thought not sure what rears you have but I know eaton does not work this way if you have a threw shaft problem the pig has to be pulled hope this may help .

 

Just keep checking the drain plug for metal. That will give you your answer.

 

Well that's what I would have thought also but none on fill or drain but there is a few real strong magnets in there so im figuring that's where the shoulder from threw shaft is stuck they a pita to clean off when a rear is apart they caught 4 heads off the ring gear bolts on my kw that had eaton rears . I would look to see if there is more than normal amount of threads of shaft sticking out it has been a while but when mine was giving me trouble I think there was a bout a inch after new shaft and bearings bout a 1/4 stuck out of the yoke nut .