I am going nuts trying to find this problem.
So far I have replaced the front U joints as well as the U joint closest to the rear. I have not replaced the U joint near the transmission yet.

When I am driving along at about 45 and the truck shifts into overdrive and then seems like it would like to shift back into a lower gear for more power..... I get this terrible vibration/grinding noise which seems like is comming either from the transmission or the rear end. I have really no idea where it is exactly comming from but just taking a guess from what I hear. The noise will go away when I let off the gas. It will also go away if I give it more gas and force it to shift to a lower gear. Is this a transmission problem?

How can I tell if the rear end is bad? It does not make a constant noise like a bad rear would.

Any help would be appreciated because as of right now I am finished sinking money into is just guessing. I would rather wait and see the part actually fall off the truck so I know exactly what it is....

 

I would have to say that if it doesn't do it except when it goes into overdrive - your tranny is shot. The overdrive unit in the tranny is a weak point in these trannys. If it doesn't do it in a lower gear, and doesn't do it all the time (rearend) that kinda narrows it down. You can take the cover off the rearend and drain the oil out and check to see if you have chunks of metal on the magnet at the bottom. If you do - it is probably the rearend. It is normal to have a powdery metal substance on the magnet, but chunks of metal are bad news. If this checks out, and the u-joint you haven't replaced is not loose, I'd have the tranny checked out at a good tranny shop. I've had tranny rebuilt twice in 60k miles.....

Do yourself a favor and change the rearend gear lube to synthetic when you pull the cover to check it.....

 

Quite a few of us have tranny's that jolt, or jerk a little bit in OD. But if you think it seems worse than it should be I'd get it checked out for sure.

 

this is much more than a jolt...
it is more of a very loud shudder noise when it is trying to shift for more power.

Do I just unbolt all the bolts on the rear pumpkin? How much fluid goes back in? Where do I buy the synthetic?

 

3 quarts is all you need. You get the syn at any auto parts store. Also pick up a tube of the blue RTV (ask them if you don't know what it is) When you but the cover back on just goop a good amount on the axle where the cover sits to seal it up. You don't want a crap load on there but you want a good amount so it will seal right. Use your judgement

 

is it called gear oil? Do I pop out that rubber plug and pour it into that hole?
sorry for the dumb questions but I have never done this on a rear before. I wonder if I had the tranny flushed if it would make any difference.

 

do you have a hanger bearing?

 

my tranny was acting up and i got the tranny flush done by a machine and it made a world of difference... i got to see what was sucked out of there and there was little metal flakes/shavings floating all around in the little glass... that was right when i bought thte truck too

another thing is if you change the rear gear fluid... if you have a LSD rearend... the tracloc rear... you have to get the friction modifier for the clutch plates in the rearend... to find out if you have an LSD or not get a build sheet... search for buildsheet in the threads and it will give you a link to input your inof and youll get a build sheet emailed a few days later... took 2 days to get mine... ALSO you can go to the dealer and they should be able to print one out for you... i would have done this but the stealership i went to was gonna charge me 20 bux... ********... anyway... your build sheet will tell you if you have an LSD tracloc rearend..if you do you gotta get the mopar friction addative.... like 12 bux for a 10oz bottle..use all of it... and add that first in the little hole on top of the diff...then add your gear fluid!