Wise choice dumping those hard kit grips, I started replacing them 50 builds or so ago with nice soft BMX foam grips.
I saved a dozen or so of the left side ones for dog toys and the rest just go straight to the trash.
They come in a couple different packages from the bike store.
The $8 package has 2 sculpted grips and end plugs.
The $12 package has the same pair plus 2 long ones. One long one makes 2 grips.
To replace the obnoxious hard throttle grip remove the throttle barrel and just cut the grip lengthwise with a razor knife starting at the inside hand stop.
Size the soft foam grip to the throttle barrel and cut as needed with the cut side facing in.
Soak the foam in some hot soapy water for a few minutes, put the throttle barrel on the ground with the end facing up, then just 'milk' the foam grip on to the barrel leaving ~1/4" from the cable hold so it clears the throttle housing.
The barrel has lateral spines and when the soapy water dries the grip stays in place and the difference in how you feel the road is nothing short of amazing, hence why every build gets them now, a world of difference in riding comfort for just a few bucks ;-}