[caverman]

From reading what you posted I think what Pete is recommending (I think most other vendors will to) is that you need to replace your sub-frame (aka: cradle) bushings.

With the HP you're probably talking about you should go to the full bushing and not just the bushing insert.

I don't have near the HP you're talking about and I put in just the cradle inserts. I could feel the firmness immediately. I felt it way more than even the Hotchkis Chasiss brace that I added.

There are several brands to choose from Pfadt, Whiteline, BMR, Energy.....but I'm partial to Pedders. Do some searching on cradle bushing inserts and then pick the Mfg you feel is the best for you.