My rear drivers side suspension is 1" lower than the passengers. Every thing looks to be in good condition. I've read in lots of different threads and forums that this is not unusual. In several factory TSB Ford suggests to shim between the leaf pack and perch. So my question is, can anybody think of a reason why adding a 1" block to just one side to level it up is a bad idea?

 

No. If the inch bothers you, fix it. Mine does the same thing and it bothers me a little too (but only since I measured it - before I didn't notice)

 

If you found a ford TSB addressing your exact issue then I would say it's probably not a bad idea. Although, that TSB is probably meant to be addressing the vehicle when it is much younger. I would think a lean on a truck as old as ours is caused by worn/rusty or broken parts.

 

I kinda thought it might be just the extra weight on that side for 20 years.

 

A rear sag can, for some reason, be caused by saggy front springs. I don't understand how, but several people have reported the rear sag being corrected when they put new front springs on. I may be remembering that wrong, but don't have the patience right now to research it, that and my internet keeps going out (probably why I don't have any patience).

 

An example. If the left front is down, it will make the right rear look high.