US stock futures experienced fluctuations on Tuesday as investors assessed early reports on a crucial earnings day, with a focus on Big Tech results as potential catalysts to sustain the year's rally. Futures for the S&P 500 and the Nasdaq 100 hovered near the flatline, following sharp gains in the previous session. Meanwhile, Dow Jones Industrial Average futures showed little change but remained in the green.

Investors closely analyzed the earnings releases of General Motors (GM) and Coca-Cola (KO), which were among the first high-profile quarterly reports of the day. Attention was then turned to the eagerly anticipated results from Alphabet (GOOGL, GOOG) and Tesla (TSLA), set to be announced after the market closed. These reports were particularly significant, as they would indicate the continuing growth of the "Magnificent Seven" tech conglomerates.

The S&P 500 and Nasdaq experienced a rebound on Tuesday, fueled by a resurgence in tech stocks. This recovery followed the substantial declines witnessed last week, which were triggered by a rotation away from the megacap stocks that had been driving the market's rally throughout the year. The return of focus to the tech sector coincided with a recent decrease in volatility surrounding the US presidential election. Speculation surrounding Vice President Kamala Harris securing delegate backing to become the Democratic presidential nominee helped assuage any remaining market concerns sparked by President Joe Biden's withdrawal from the race.

Turning attention to individual companies, Coca-Cola emerged victorious in a comparison with its competitor, PepsiCo. Coca-Cola's second-quarter results revealed a 15% increase in organic sales and a significant rise in operating margins year-over-year. In contrast, PepsiCo's performance disappointed, with no comparable sales increase and lower operating margins. Furthermore, Coca-Cola revised its guidance upwards, while PepsiCo did not.

General Motors continued its positive trend by once again raising its annual profit forecast after exceeding expectations in the second quarter. The company now anticipates full-year adjusted earnings of $9.50 to $10.50 per share, up from the previous projection of $9.00 to $10.00 per share. General Motors' second-quarter earnings beat estimates by 31 cents. In terms of EV production, the company reiterated its goal of manufacturing 200,000 to 250,000 electric vehicles for the year.

However, UPS faced another challenging quarter, which caused sentiment towards the company to decline. Similarly to FedEx, UPS experienced a shift in perception, with FedEx viewed as a promising investment due to its cost-cutting measures, while UPS struggled with disappointing financial results. UPS's morning report included a reduction in operating margins for the full year, which is likely to be poorly received by investors.

Overall, the market remained cautious as it awaited the outcome of the Big Tech earnings reports, which had the potential to influence the continuation of this year's rally. Investors closely monitored companies such as Alphabet and Tesla to gauge the sector's growth trajectory.