front end shake @ 55-65 mph

Hello all! I have my beloved wagon. Today I replaced the steering damper and checked the torque on the wheel bearings (12 lb/ft). Friday I had the wheels balanced and they said that the tires are good. I hopped in to take my wife to the movies (Starsky and Hutch, for the Torino) and it came back, only not nearly as bad. The shop also told me that the front end looked tight to them. I tried the 4 p's earlier and all appeared well to me. I need some ideas. Im almost thinking that its the ball joints. Straight line driving, I get "the shake" at 55-65 mph. When going around corners and such, "the Shake" disappears. This is what keeps me up at night. Any tips, help, ideas, sugestions, anything would be of great help. Thanks in advance.

D. Herman

1990 300TE
1993 300SE
1994 Chevy S-10 (Wife's Truck)