1986 Chevy Monte Carlo shaking side to side

I have a very bad shake, i've tried everything I can think of to fix it. The car sat almost a year with a bad tranny, after it was repaired the shake began, i've replaced tires and rims, got alignment, checked idler arm, pitman, tie rod tranny mounts, engine mounts and even replaced coil springs. The only thing i've noticed is a leak at the pwr. Steering box. I've checked for wollowed out nuts, bolts, and even had the frame checked. Please help, I miss my car. Paula p.S. U-joints were also changed.