Your sort of right
"posi" is a term from chevy's positrac which is their version of what dodge calls a limited slip differential (LSD).(I forget what ford calls it). neither are a locker but accomplish the task with clutches and pressure instead..

 

Ok guys I just checked the motor mounts and the transmission mounts and there was no movements when it was In gear with the brake held and torqued pretty good and NO movement at all. I have noticed in the mornings when I first get in it to go somewhere. I took the truck out yesteday morning and drove it about 30 miles and it didn't have alot of vibration or wobble. So I headed back out of town later that day with my wife we got about 5 miles out and it started the drift and it felt and sounded like the rear end was wobbling like the rear lug nuts might have been loose or the axles were gonna come out jst like the other day. I checked and double checked everythig for tightness and eveything is tight. I checked the drive shaft to be the U-joits aren't bad and when I twisted on it it barely moved less than 1/16th of an inch. this is really frustrating me since I have put a brand new motor, brakes and all new brake hardware all the way aroud the truck, and on my rear end when I jack it up and spin the tires both rear wheels spin in the same direction.

 

Check your rear brake adjustment..... Make sure that your front brakes are releasing properly after you take your foot off the pedal.....

I had a customer truck with the same problem...... normal around town stop and go driving, everything was fine... but, get it somewhere that you could cruise for a while, and it would start shaking like an epileptic. Turns out, the drivers side rear brake was adjusted a bit to tight, and it would overheat the drum, and it would then warp..... violence ensued... let it cool for a bit, and the problem would go away for a while....

 

I checked to see if the brakes were hot after driving it for a while and they were normal. I tried shuttig the overdrive off and it was still the same. I did figure out the pinging noise which is an easy fix the fan is hitting the shroud. I'm goig to attach pictures of my upper ball joints if somebody could tell me if it looks normal to you cause they don't look normal to me thanks guys.