WileyE,
What you experienced is common for most cars - trucks as well. Decreasing understeer makes a car feel more nimble and responsive. You can accomplish this by increasing the inflation pressure in the front or by decreasing the inflation pressure in the rear - or both, like you did.
Unfortunately, when you add cargo in the back, instead of having a tiny bit of understeer, you have oversteer, and that is not only difficult for the average driver to cope with, it is also more dangerous.
One word of caution for everyone reading this thread:
Tires are much more prone to failure the less pressure you use. Be cautious if any of the methods you try result in an inflation pressure below what is listed on the placard - and the further away you get, the more cautious you should be.