My GF's Duster 360 is slow as hell !!!

Get a 10" 3500 stall converter.A mild 360 will have a hard time brake stalling a 3500 to 2800. You need at least 2800 to get it to perform . Most all good running 340 cars I have had with the factory converter brake stalled at 2800 to 3200 depending on how stout the motor was . I found 3500 replacements to be the closest to 2800 in a small cube motor. A 440 will brake stall alot Higher with the same converter and flash stall even higher. Check your stall by applying the brake hard . Floor the accelerator without the tires spining. and see where the tach stops. This will be your stall. Lower than 2500 get a new converter.