yea only thing i havent checked is the wheel alignment, but i could have swon the mechanic said it was good when it was there but i know he didnt have a rack.? could my correction kids on the front the camber kits be loose??

 

Its gotta be something that is effected when only under load. Its most apparent under HEAVY load correct? If you ease it up to 50mph at say 25% throttle, its not evident correct?
Are all your axles new? Ive gotten reman ones from the autoparts store and they shook as your describing worse than the broken ones. I think your problem lies in the CV joints having to much play/clearance. Know anyone that you could borrow their axles to see if it makes a difference?