84 k5 driveline vibration

[Jordanc]

so i recently picked up a 84 blazer thats got a 4 inch lift, i really dont know much at all about the truck, what i do know is that it has a 350, with a th350 transmission, not sure on the transfer case, but under acceleration its got a pretty good vibration, letting off the throttle it does go away, kinda stumped on this one but i do know the drive shaft in it for the rear is not factory

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[RoryH19]

Looks like a np208 transfer case.
The rear driveshaft is not original, looks like they put a SYE with double cardan joint. Really don't need one for a 4" lift but it's an upgrade.
Also noticed the axle yoke appears to be pointing down instead of parallel or slightly up.
You will need to check drive shaft angles.

 

[Jordanc]

to be honest i looked at it again today, and it doesnt look like it has a sye it looks like a sye thats put in to a slip yoke im not sure if thats right