I've never seen those dump trailers pulled by anything less that 3/4 ton trucks. So I personally wouldn't do it with a Taco.
Top soil can vary quite a bit in weight. I take it that you are buying it some place that loads it for you. Just get out of your truck and watch as they load it. Tell the guy running the loader to watch you, that you will give him a signal when to stop. That way you can judge how much the load is compressing your springs and stop where you feel safe. Yes do several smaller loads it will be better for your truck.