This phase I trial studies the side effects and best dose of calcitriol when given with cisplatin and gemcitabine hydrochloride in treating patients with advanced solid tumors that cannot be removed by surgery. Drugs used in chemotherapy, such as cisplatin and gemcitabine hydrochloride, work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Calcitriol may stop the growth of tumor cells by blocking blood flow to the tumor. Calcitriol may also help cisplatin and gemcitabine hydrochloride kill more tumor cells by making them more sensitive to the drug.