When I let off the gas it completely goes away, which is why I was ruling out power train, as in theory, it should remain a constant shaking, which is also the same with the wheels. I'm stumped, like I said, all suspension parts are in great shape and tie rods and ball joints are fairly new.
It started when I was getting on the highway hitting about 60 mph initially, so I am ruling out bent rim, but this I suppose could also be the culprit, yet it would do it whether it was under load or not as it would still be spinning.
The tranny is new and in great shape
The passenger axle was replace just over a year ago, so possible that it could be the culprit but when tested from under the car nothing jumped out as being wrong, where the drivers side on the other hand was noticeably messed up.

I was hoping the engine mounts, as it's a cheap and easy fix to replace, and they are moving a bit more than they should be and thought it was explainable as it was happening under load, but again the constant start point of 60 kmh is throwing me as well, as if it was the mounts it should again in theory, be there all throughout the drive range as it is always under load when accelerating

 

I wish I knew what to suggest, it sounds very frustrating.
I had a problem a few years ago with shaking, but it was only while cornering.
2 shops plus my dealership couldn't find it. I had a broken bolt on the rear camber adjuster, so the wheel was flopping side to side. With my big tires, it would hit fender if I turned and hit a bump. Finally, I went for 4 wheel alignment and they found and fixed it.
I'd suggest an alignment, not that it needs it, but just as a diagnostic to see if anything is out of place.
Good Luck. !!

 

Just an update for anyone reading this post, the problem has been fixed, it was a bad inner cv joint causing the shaking and I replaced the passenger side axle and the car is driving like new again. Thanks for everyone's input. I did a lot of research and trial and error, as I was going by the wrong advice from my local canadian tire mechanic who diagnosed the problem as the drivers side axle, but in the end I have a completely new front end in my car now so I'm not too upset.

 

I'm glad to hear you got it solved. Hopefully mine will be fixed in Monday.
I'll see what they charge for parts, I go to Aamco, but he has no problem with me buying the parts, and Partsource is right around the corner.
I used to buy a lot of parts from Rockauto, but they've given me the wrong part a few times. Be very careful, they don't seem to recognize the SS uses different parts than the Lt.

 

Glad to hear that Ken, you and I both have had our most recent problems solved this week!

 

Ken
Glad you got your problem solved and it's driving like new again!!