Just bought a GQ last weekend and I'm working through all the bits and pieces. It had a massive shake in it because my 2 previous cars (Rangie, Rocky) had a shake like this before I even looked underneath it I bought some panard bushes and bunged them in, that helped a bit, shake still there not nearly as bad, spent a day doing the swivel hubs, and hey presto no more shake.
I suggest anyone with a shake like this to look firstly at panard bushes (cheap) and secondly jack one front corner of the car up grab the top and bottom of the wheel and see if there is any movement any movement there indicates wore king pin bearings which either need to be replaced or shimmed to get more preload, I got a Swivel Hub kit from REPCO for $250 and they do both sides include bearings and axle and all other seals and gaskets, I wouldn't know how much a grease monkey would charge to put them in coz I did mine myself. But I'd say add another 300-400 on to the price of the parts