truck Shakes/Vibrates at higher speeds

hello, i installed another rear end because mine shit the bed, and now when i go above 55 mph sometimes my truck shakes extremely violently, others its barley noticeable and sometimes it rides smooth. does anyone know what would cause this? driveshaft misaligned? or something wrong with the rear end i put it, the salvage yard i got it from popped it open and said it was in good condition. all input is appretiated. thanks

 

Describe the shaking more. My truck shook at certain speeds but it just needed the tires balanced. We need more info to really help.

 

Check your driveshaft, check your carrier bearing, check rear end bearing, and are your tires balanced?

 

had tires put on and balanced 2 weeks before the rear end was put it and it was fine, the shaking is hard to explain. it feels like the whole cab is moving around even though its good and secure. the shifter shakes back and forth. i can hear the dash moving. i can feel the shaking in my cheeks. its as if some one grabbed you and shook you.

 

it doesn't sound like a rear end problem to me. have you checked your inner and outer tie rods? I would start there.
Get your front wheel in the air and try and move it side to side. It shouldn't have any "play" in it

 

alright will do, i was thinking it was because it was fine right up until i got the new rear end in.

 

jacked her up, no play in the tires. both shafts are nice and solid.

 

Try unbolting your driveshaft at the rearend and turn it 180 degrees and bolt it back toghther. Do you know what I mean? Also check that your leafspring bolts (ubolts) are torqed to 100 pounds.
good luck. I hate rear end vibes