It's doubtful that a worn steering shock would cause the problem you've described, but checking the shock for wear is easy. Just unbolt it at one end and pull it out to it's fully extended position. Then, push it back the other way. If it's leaked any hydraulic fluid it will be very easy to push in. If it moves easily for an inch or two and then offers some resistance it's unlikely that is the cause of your problem. Don't overlook the rear suspension as a possible cause. When you floor it to the point of "kickdown",if worn components in the rear shift due to load, this changes the vehicles "thrust angle". In order to offset this condition you would have to steer the car to maintain direction. This could explain the sensation of swerving. Also, take a look at the transmission mount and, although unlikely, check the driveshaft center support. Good luck, and let me know how it works out.