Hi, my '97 x-90 runs well but when i get on the highway and go the thing shakes like hell untill i get up to a faster speed , enough to shake the dash . I can't find the problem with this. I did the front end alighnment by eye (for now) but can't see that causing it to act this way. I can grab my rear shaft and move my tranny back and forth alot , could it be weak mount causing this vibration ?  don't know where else to look.  I should mension i just installed a new 6" calmini combo lift.  Also when in 4x4 low it doesn't do it at all , even going through the gears on highway.

thanks!

Shake or vibration? high speed vibes is driveshaft, shaking is more of an
out of balance thing, like tires and yes, after your lift soft old bkoken
trans mounts could be allowing too much movement, but we need
more description of the problem

Wild

Its not high speed vibration as higher speed is better in this case. Its like something in the drivetrain is vibrating like an axle or joint problem  it shakes the dash when starting out on the highway going through the gears. It seems to kind of go away after i'm up to speed on the road.  It doesn't do it in low range 4x4 . Also i can barely reach 60MPH flat out running 31's does this seem normal for a 1.6 l motor ?

By high speed, I mean the spinning parts, but I get your statement.

Sounds like it could be Bias ply tires, they have a habit of flattening
out when they sit for a while, does it get better after running for a
while? or is it the same?

 Same all the time , tires are BF's mud terrains like new , don't think its them causing it , even at a low speed while excellerating the vibrating is there , its not like metal on metal noise or joint noise, not much noise at all really just feel the shake/ vibration through the whole car. , i know its hard to diagnose  without seeing i guess i'm just looking for ideas to try .  I can grab the rear shaft and move it back and forth at least 4" side to side at rear of trannt by mount , this could be some of the trouble maybe a weak mount.

That would be a broken mount 4" is a lot

I would say the lift is causing some minor binding in the drive shaft
and that is moving the trans around because of the broken mount
and giving you your problem, start with the mount and see where
it goes from there. I would say a spacer or slip yoke eliminator with
a DC drive shaft would make it all go away

I have a 1" spacer on the shaft that came with the calmini kit , what is a slip yoke eliminator ?  and you mean a double carden shaft with two joints on one end ?
 The mount looks fine just looking at it , i mean i can prolly move the shaft 2" on each side back and forth , i can watch the movement is in the rubber on the mount , hopefully a new mount would be much firmer.
thanks

Slip Yoke eliminator is a replacement for the drive shaft/trans connection,
in stock form the drive shaft has a slip yoke, that slips in and out of the
trans as the suspension moves through it's cycles, the eliminator puts a
flange on the end of the trans, Samurai style and the drive shaft has a
slip spline, again like a Samurai does, and if you are doing that you might
put a double U-joint (DC) in there since you are building a custom shaft
anyway

Ok  thanks i will give it a go !  very helpful !