Since you're bootlooping into fastboot, you can try download 8T Fastboot ROM to unbrick it ( if ur bootloader is unlocked ). If not, besides of using testpoint on the mainboard, you can purchase deep-flash cable ( around 2-5$ depends ) it can help u to boot into EDL mode ( same effect as using testpoint ), then use MSM Download Tool ( which specified for your 8T variant ) to rescue ur device!