Washington Cycle is a great shop. They are my go-to shop for 'on the road' tire swaps for any New England runs. They have performed short notice tire installs and also ordered tires for me by phone to install the next day. Don't remember the owner's name, but he helped me out in a pinch and it deserves mentioning.
Bear in mind, the spring swap alone will help with the sag issue, but will not improve the shock performance. Just sayin.
I've used the Tusk model on a few springs and it does a good job. Be sure to keep the threads well lubricated and keep the load well balanced.
