Lookin to put in gear oil in thr rear

You have to determine whether its just thr brake parts rusted or the bearings in the rear end and axles. Drain the gear oil from the rear end to see if there's any water in it.If it seems ok then put new gear oil back in and try this: Jack both wheels off the ground and put it on jack stands. Try breaking it loose by rapidly changing gears from reverse to drive and stomp on the accelerator. If it breaks loose that way it will be easier to get to the brake parts to see what needs to be replaced.

check and see if ur get fire and gas ur not getting one

if its manual shift then inspect the linkage, if its push button then the motor/servo on the transfer case could be the issue. or the switch. i had to chase a simular issue on my tahoe and it ended up being the motor on the transfer case that selects the gears

Sounds like a bad ground to me, although i am no expert.
i would be checkinh all connections and take it from there, a little wd40 might just solve it short term.

Hello my name is Ben. For your truck you will use SAE 75W90 synthetic gear oil in the rear.

Put rear tire's on jack stand's, remove left rear tire, brake caliper and bracket and slide off brake rotor, then remove rear end cover get a pan for fluid to drain into,there will be a set of gear's through the gear's on the right side of the ring gear there will be a pin about 13/4" in dim. and about 5" long at one of the end's there will be a small bolt that hold's that pin with an 8mm head going through it, remove that bolt,slide pin out, go over to axle push in (do not turn axle) go back under truck remove horse shoes clip at end of axle, then side axle out, install new axle and refill with gear oil some take a anti-slip additive.Goodluck

it is right next to the fuse box next to the inner wheel well next to a small black square box on either left or right side.

As with any transmission nowadays, keep it serviced regularly, and make sure it has a good external cooler, not just rad cooled.

get under truck go to the back of the rear-end housing shoul be a plug u can take out and u can kinda see in you can add the gear oil in that same hole you can only add oil up to the bottom of hole then put plug back and go on to next project

If noise was not there before the gear change I would say that the gear are not set up correctly. Have the shop or person that did the gear swap recheck the gear backlash and the pattern on the teeth.
Too much heal or toe on the gear mesh will cause a decel whine or an accel whine. May just need to reset the tolerances on the gears.May be best to have a reputable shop check and reset the gear backlash and pattern. This is not much af a DIY type project unless you are experienced at doing gear work.

Hope this helps