It's the same. Sources suggest that tall 2X size can be labeled as 2XT or 2XLT. Depending on the manufacturer, they will use a different format for big and tall.
Generally, tall sizes are longer in length and less fuller in the body compared to a big. As per Kohls.com, if you are 6'2" or taller and your waist measures less than your chest, you should order a tall size.
Tall sizes are designed to be two inches longer in length than a regular sized style, and the sleeves will be one inch longer. For best results, take body measurements undressed or in lightweight clothing.
Check out some tips for helping men make sense of big and tall at Josbank.com.