The P0700 is generic.
P0741 relates to the torque converter clutch solenoid. it is not disengaging properly and the car is seeing a mismatch of >200 rpm between the torque converter rotation speed and the transmission input shaft.
Check wiring. Was clutch solenoid replaced/rebuilt as part of your mods?
From what I can see the higher stall speed on the new TC should not be the cause of this.
Might start with a call to circle D:
https://www.circledspecialties.com/