yes the sub frame is the first place to look....that also is a key link to your rear alignment....then the spring cups for sag....but all in all its 20 years old...

not as a plug - but if you want new springs i have a set brand new that i could sell to you - they are sitting in my shop gathering dust....bought them when i lowered mine, ended up using the lowering springs with thicker cups....

good luck
Jake