It's weird, my shifter still centers to neutral, but the resistance to the left (1st/2nd) is almost nothing, while the resistance to the right (5th/reverse) feels good. I thought there was only one centering spring, what could cause this?

 

The centering spring that wraps around the shifter block moves the shifter from 1/2 to center. There is also a ball and spring that returns the shifter from 5/R. The latter of these two provides much more resistance.

 

Let me guess, the one for 1st/2nd is the one that's actually in the transmission.