Wouldn't hurt to also check that the u-joints on the driveshaft line up. New doesn't always mean good and that's a newly introduced variable.

My experience is the same as Al_Alguire. Broken tailshaft almost always due to the driveshaft. (specifically approaching critical speed or imbalance)


69 Charger. 438ci Gen2 hemi. Flex fuel. Holley HP efi. 650rwhp @7250 510rwtq @5700