Social media darlings AMC Entertainment AMC.N and GameStop GME.N also extended their rally into a third week. By Ambar Warrick June 8 (Reuters) - U.S. stock index futures fell on Tuesday as investors stepped back ahead of key inflation data later in the week, while Tesla gained on strong sales in China, a major market for the electric carmaker. Tesla's shares TSLA.O rose 2.6% in premarket trade after sales of its China-made electric vehicles surged 29% in May, data showed.