GM ( GM) gained 0.3% to $34.10 after reporting a 6% increase in U.S. auto sales for June. "We have good momentum heading into the second half of 2013: the economic outlook is solid and our launch vehicles are performing well in the marketplace," General Motors said in a statement. Ahead of the announcement, General Motors and Honda ( HMC) announced today a long-term agreement to co-develop next-generation fuel cell system and hydrogen storage technologies, aiming for the 2020 time frame. Honda added 1.3% to finish at $38.03. Dialysis services provider DaVita HealthCare ( DVA ) tumbled 6% to $114.00 after investors became concerned about possible Medicare payment reductions that might be in store for the company after the Centers for Medicare and Medicaid Services suggested Monday that a 9.4% Medicare rate cut be applied to these types of services. Follow @atwtseWritten by Andrea Tse and Robert Arenella in New York >To contact the writer of this article, click here: Andrea Tse.>.