Stocks were modestly higher in midday trading Monday. General Motors (GM) celebrated a significant milestone: the automaker has built 500 million vehicles globally. GM’s reputation took a hit last year after at least 51 death claims were tied to a defective ignition switch. The company had been aware of the problem. MGM Resorts (MGM) tumbled after reporting an 11% decline in quarterly revenue. The casino operator has suffered weaker performance in Macau. Stocks were modestly higher, boosted by improved factory activity in March and ahead of speeches from the Chicago and San Francisco Fed Presidents later in the day. The S&P 500 was hovering at its previous record closing level. Factory orders in March climbed 2.1%, increasing at their fastest pace in 8 months.