This phase II trial studies how well giving rituximab together with combination chemotherapy works in treating patients with previously untreated high- or high-intermediate-risk diffuse large B-cell lymphoma (DLBCL). Monoclonal antibodies, such as rituximab, can block cancer growth in different ways. Some block the ability of cancer to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them. Drugs used in chemotherapy, such as cyclophosphamide, doxorubicin hydrochloride, vincristine sulfate, and prednisone (CHOP), work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Giving more than one drug, combination chemotherapy, may kill more cancer cells. Giving rituximab together with combination chemotherapy together may be an effective treatment for DLBCL