general problems of the 1999 Chevrolet Astro

I purchased replacement tires for a 1999 Chevrolet Astro on this date. The dealer firestone tire & service centers, 7950 e speedway, tucson, az 85715 represented the tires as suitable for my vehicle. After I got home I discovered the tires, firestone fr380 p215/75r15, were rated for 1742 lbs at 44 psi but this should be reduced to 1585 lbs when using this tire on a truck or multipurpose vehicle which, I assume, would pertain to a van as well. The tire just meets the minimum requirements of the van which is a load capacity of 1575 lbs. But it meets the requirement only when inflated to 44 psi. Chevrolet recommends a tire pressure of 35 psi and when the firestone installed the tires they inflated them to only 30 psi. I increased the pressure to 44 psi since only then would the tires meet the van specs. I tried to get the dealer to upgrade the tires about 25 days after I bought them but they said they met the requirements of my van. Later when I went in for an oil change the change said the tires were over inflated and reduced them all to 35 psi. I am very concerned that the tires are not safe but cannot get consistent advice nor any action from the dealer. Does the nhsta have any standing in such a dispute ?.