What are you doing with the gasket?
How did you clean the inside and remove the metal build up on the magnets?
I have zero mechanical experience and not afraid to say it. I'd rather be straight forward and learn and do it the right way versus act like a BA who can do anything and screw something up.
No worries bud. But it is honestly a piece of cake. As long as you have a socket set you will be good.
To start, remove the fill plug. and have a pan under the diff. from there just release the torque on all the bolts, going in a star pattern like you do lug nuts. Then start removing the bolts starting from the bottom.
by the time you get to the last bolt, all of the fluid should have drained. Remove last bolt, and cover from the truck.
I opted to simply wipe the inside of the diff cover with a non lint rag (Or an old T shirt), and did the same with the plug, as i believe it was magnetic.
Then look at the locker magnet. you can find pics of this in the thread i linked. I just used a few Q tips to get this crud off, and wiped it down with the rag. i also shoved the rag in the bottom where some old fluid had pooled. I did not use any brake cleaner. Didnt see the point.
The gasket i can guarantee you can re-use. But please check it for cracks, or splits.
Put your cover back on, and put the top bolt in, just to locate it. Do the same for all other bolts, and then start tightening in a star pattern. I think the torque spec is 25ftlbs. But i just used a 3/8 ratchet for everything, and didnt go CRAZY with it. (I also checked them the day after).
After that, just fill the diff through the fill hole to like a 1/4" below the hole. (I just filled it up until it started weeping out the hole, then absorbed a little extra with a paper towel.
Put the fill plug in, and repeat for the front (Will take less fluid).
For amsoil. you will probably have to order online. i managed to find some diff fluid, but motor oil will be harder to find.
Let me know if you have any questions.