I have a 1988 (1987 chassis), and it was always a white knuckle, E-ticket ride at anything over 60mph. Then, after weighing the rig, front and rear, and looking at a tire pressure chart, I realized that while I was running about 55psi in all 6 tires, the chart recommended only 45psi in front (rear was good at 55psi). So I dropped the front tire pressure by 10 psi. Wow! It made a huge difference! While still not great, I can actually drive with one hand, comfortably now.
My point is to start with the cheap and easy things first (it doesn't get any easier or cheaper than air pressure!). Make sure those are taken care of before spending money on alignments, steering boxes, bushings (unless obviously worn out of course), sway bars, etc.