also you may want to check you rear u-joint going into the rear diff and check the pinion bolt tightness. make sure it is tight and if its not look into replace the pinion bearing. and check play in you axle shafts

 

I had a '98 SLT with the same exact problem. It had the posi rear end. I took the pumpkin apart, maybe 1500 miles after changing out full synthetic gear oil and friction additive and my gears were all stripped apart. Do what you can to save your rear end. Like everyone said, buy the friction additive and if that doesnt work, pray that you dont need a new rear.

 

i have a 2006 dodge ram trx4 offroad it makes a chutter noise when i take off in a strait line but goes away when i turn i just had all bearing and seals replaced in rear end he did put the correct lube in it he told me to do some figure 8s in a lot it should go away he said who ever did it befor never put in the additive but why does it do it in a strait line.