I just finished putting a turbo 400 on my stock 305 engine with stock torque converter and now it stalls when its under load...do I need a new torque converter that matches the TH400??

 

What do you mean by stall (engine quits?)(trans slips?) and what trans is the torque converter from?
You didn't give much info here,how are we supposed to know?
The 350 and 400 trans both take the same converter so if you went from a 350 to a 400 it shouldn't be an issue with that.
Is the motor stock or cammed up?
Is the trans rebuilt or used?
Is it high stall converter or stock?