So, Rosie leans...
 

Well, the title says most of it. She leans to the driver's side. It looks to be about a one inch difference between the passenger and driver's side. It is throughout the whole side.

Where do I start looking to determine the issue?

She's a '68 LWB 1/2 ton stepside, if that matters.

Re: So, Rosie leans...
 

I measure the spring height of all 4 springs as it sits on level ground [compressed spring height ] to check for spring sag. Do not rely on measuring top of fender to ground because you may have bad cab to frame mounts. If the front springs are close to each others and the rears are close start checking cab mounts

Re: So, Rosie leans...
 

My guess is sagging driver's side springs, and possibly worn out suspension bushings. At 45 years old, who knows how much of its life was spent with a driver and no passenger.

Re: So, Rosie leans...
 

If I need to replace the springs, can I replace them with 3/4 ton springs? I will eventually tow a camper or have a slide in camper. It's currently a stock 1/2 ton.