Does the drive shaft need to be in time? on 1995 Chevrolet S10

I replaced tran and diff seals, there was no vibration before the seal replacement. now a noticeable vibration. checked rear u-joint saddle for miss alinement, but is in correct position.
Vibration subsides some after 65mph.

Asked by for the 1995 Chevrolet S10
If you replaced the pinion seal, did you torque the 'yoke' retainer nut correctly?
I torqued it at 140 '#
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1 more answer , 5 more comments
if its one piece drive shaft no it doesn't,double ck you work b4 you damage the diff gears
It's not a 1 piece shaft...has a slip joint and mount mid way back from trans
Long bed pick up would have been useful info! Bunch of S-10's!!! All u-joints have got to be in line with each other! Did you separate the shafts?
it's not a long bed, but is extended cab and all joints are in line
Same difference!! No other way to "time" a u-joint.
I called a Chev dealership and there service dept said it needs timed...remove rear joint from saddle and turn diff yoke 180 deg