O/R Megacap growth and technology companies such as Apple Inc AAPL.O and Microsoft CorpMSFT.Oeach roseabout 3.5%, while banks <.SPXBK> advanced 3.1%. By Echo Wang Oct 3 (Reuters) - Wall Street's three major indexes rallied over 2.5% on Monday to start the final quarter of a tumultuous year in which investors fretted about aggressive interest rate hikes amid historically hot inflation and fears of slowing economic growth. Data showed manufacturing activity increased at its slowest pace in nearly 2-1/2 years in September as new orders contracted, likely as rising interest rates to tame inflation cooled demand for goods.