[fredjacksonsan]

Well it sounds like you're overloading the Jeep. I think Cherokees are rated for about 800 lbs of cargo including passengers. With 5 people + 400 pounds, you're over that, and WAY over if they're big guys. Even though it's only 4 miles...

Your post begs the question: why drive 400lbs every day? Why not leave it in the storage facility?

In any case, with any spring upgrade that would handle the load, you experience a much worse ride quality probably.

More importantly, your maximum load isn't based just on springs, but also on axle capacity and the body of the vehicle. Even if you installed HD springs , the axle/hardware/etc would be taking the punishment and might not last long.

Best solution IMO is to get a truck(pickup) if you'll be hauling those kinds of loads on a regular basis.