I too have never had to put a return spring on the KD lever, even when using a cable. The throttle valve has a internal spring that should do the job. By your description of the shift timing I doubt you need one.
Does it still shift soft into 2nd gear? What ratio front band apply lever did you use? If it's a stock 2.9 lever upgrading it to a 4.2 should improve the 1-2 shift quite a bit
