I went to have my rear u joints done and the guy bent the pinion ...I couldn't get him to fix the problem and he refused to finish repairing the truck...I need a quick fix for leaking rear differential...its leaking from the cap seal....is there a heavy gear grease I can use as I have to get home asap...its roughly 250 miles.

Take it back to the dealer. The problem could be a Constant Velocity Joint wearing out.
Replacing the rack and pinion is an exceedingly expensive repair. Replacing a CV joint or axle is significantly less expensive.
It sounds as if your dealer is honest.

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If you are definitely sure it is coming from the rear end you have to remove the rear end cover. You will see the condition of the fluid check the fluid while that is being done. You will have a bird's eye view of the condition of the ring and pinion gears and the pinion bearings. The rumble from the rear end is usually a bad pinion bearing.

If you're not sure it is the rear, another often overlooked problem is the rear universal joint on the drive shaft. You have to remove the drive shaft to check the pinion bearing so you'll find the "U" joint is bad right then and there. If the joint is bad, don't cheese out, get both of them replaced.

find a mech with an electronic stethoscope.
$50 tool/
we can find any noise. source with this
except U-joints. on main drive shafts.

find a pro mech, they all know this.
Id put in new U-joints if , all my electronic hear tests pass/
see that logic?
i check axle ends, and pinion front bearing.
and engine , and tranny front center and rear.
all normal.> then U-joints are bad.

most guys just put them in , to start. can save time.
warning, all tests here are dangerous. that is why use
my remote monitoring stethoscope with zero risk .
person 1 drives, i rind shot gun and with head phones on
i stop and move my microphone clamps
takes about 30min to 1hr to finish a test.
my last catch, was a bad right axle bearing, RR.
i caught it early.
sounds can telegraph, so lots or listen points, prove who is the offender.

Out of balance tires or a bent rim.

Sounds like one of the calipers are not releasing when it should. One could be releasing correct and when you take off the wheel causes the other to release causing the clunk.

Does "clank occur when shift fwd/rev ? Worn U joint. Can be hard to change. DIYrs bash it out with hammer(after removing driveshaft from truck) Techs use press. These trucks prone to rear flange splitting @ U joint cap. Drive shaft bearing ? :"It dont got 1" Pinion bearing in diff supports driveshaft. sometimes pinion flange nut backs off, but usually worn pinion bearing causes it to seem that way.
Block wheels,trans in neutral,crawl under and rotate shaft by hand. Listen for noise.Follow sound to movement( there should be ALMOST none.Where 1 part moves and the part attached doesnt,,theres your prob. btw "drive shaft bearing USED to be a joke.

sounds like ya a-arm or bearings goin out

8 months of trauma! The original d/s has a double Cardan style...other wise known as a constant velocity u-joint, at the pinion end/rear end connection. My Ford dealer had it to the d/shaft re-build place and they did a new d/s w/single u-joint at the rear end. WRONG! The OEM shaft has a needle zerk on the Cardan joints and most shops don't know about it and don't see it and so it never gets grease. What you need to do is just re-build the original c/v Cardan and the prob. goes away. My dealer finally installed a double/double Cardan d/s!!! $1200. NO CHARGE TO ME! Problem solved! The OEM as I recall, has a double cardan at the rear end only. This one has a double at the hanger bearing and at the rear end!! I also installed the S-10 extended cab drive shaft alignment kit from Stealth Conversions. They claim even if you have the double cardan this kit will make it last a lot longer. $42. for the kit and $200 for the install by my gar. guy. I would have done it myself but the bolts on the rear end needed to be heated to get them off and install the 2 degree shims. No way I'm laying on the floor w/a torch 2 inches from my nose to do that!! Now it is as smooth as silk! What an ordeal! This is the ONLY way to solve the vibration problem. You need,at minimum, the OEM double cardan (C/V) system at the pinion connection. You probably don't need the double at the hanger bearing. Hope this helps.

Your carrier bearings and possibly the pinion bearings are the source if the noise is a low pitched grumble or gravelly noise that starts just about 20 mph and up. If it is louder when quickly changing lanes to the left, it is probably the right wheel bearing, and if it is louder when changing lanes to the right, it is the left wheel bearing. If it is a whine that is really annoying at 45-65 mph, your ring and pinion are probably worn beyond their design specification limit. If your U-joints are OK, but you can hear a loud clunk from the rear when you get on and off the throttle, you definitely have play in your ring and pinion. Have the cover removed and you can sheck this easily. I have worked on several Jeep Grand Cherokee differentials, and the ring an pinion has needed replacing on them all. A few had bad bearings, too. You should probably replace the bearings and the ring and pinion, because the labor is nearly the same and the parts are just a bit more. If you look through the forums on the www you will find many people that replaced the bearings to fix the grumble, only to finish the job and find out they also have the whine.