Gst shakes when doing pulls

[Lightnintko]

Ok, I got a 99 Gst, my first turbo car! 168k
Manual Transmission shifts ok / engine runs normal no check engine light.
Runs great whenever I'm driving normal.
I was driving on the highway @ midnight and decided to test out how fast it can get up. When I put it into 3rd going at about 75 it starts picking up speed nice, but then it starts shaking moderately. The shaking doesnt seem to be any steering or balancing problem because if Im not flooring it i can get it to high speeds no problem. Alignment is perfect too. Also, when I was in 4th gear (by that time i was close to 100, I let go off the gas and as I push the clutch, I barely have to touch the shifter and it pops into neutral faster than normal. This 4th gear pop has happened to me in normal highway speeds too. It only happens if i'm accelerating a lil hard. Almos Feels like it wants to get out of 4th when its under moderate acceleration.
Any toughts?

Oh, its also bone stock

 

[Kyle_T]

Does it sound like this? (Skip to 0:45)
Driveshaft 101 - Parts, Tools & Tips - YouTube

 

[Lightnintko]

Does it sound like this? (Skip to 0:45)
Driveshaft 101 - Parts, Tools & Tips - YouTube

Its a gst (fwd)

 

[Anthony95TSiAWD]

I was running spark plugs that were to hot and was getting a shake/hesitation under wot but ran fine under normal throttle. Then with forth gear popping out mine was also doing that, i had bent a shift fork.

 

[rEclipserGST]

Its a gst (fwd)

So0o0o? Does it shake like the video he posted or not? Geeze

 

[Lightnintko]

I was running spark plugs that were to hot and was getting a shake/hesitation under wot but ran fine under normal throttle. Then with forth gear popping out mine was also doing that, i had bent a shift fork.

I will check the spark plugs I haven't had any time since I just got the car; that'll be one of the first things i do. Also you have any more information on the bent fork? What is that, the bar that links the shifter to the tranny?

I was also considering the engine and trans mounts.
Would these cause such symptoms?

 

[Anthony95TSiAWD]

It was the shift fork on the 3-4 slider.

 

[Lightnintko]

I think i found my shaking problem. I put the car on jackstands and made it freespin.. it shakes horribly!! It looks like my tire is unbalanced(maybe bad rim, balljoint is shot) its now in my to do list

 

[Insane20]

Put the bent wheel on the rear. See if the shake go's to the rear. Then you will know for sure what it is.

 

[4g63ej257]

Shaking (under accelerateion) especially in fwd alot of time will be a bad cv joint .

 

[kenuwine4g63]

What about the wheel bearing? Se of you can shake the tire without spinning it, if it shakes then the wheel bearing is bad

 

[needbooost]

I had a very similar problem in my gsx, it was a bad injector. When you drive easy no shake but you go wot and it shakes terribly.
A bad motor mount or axle can cause a lot of vibration as well, if you pop the axle out of the hub you can spin the hub, if it spins with ease its trash if the cv joint doesn't move well it could also be bad.