Also check the contacts on your switches to see if they're adjusted properly. If they're too close they could be sticking together for a bit.
I had a slingshot sticking on my Bride of Pinbot and the screws that hold the coil assembly in place had come loose a tiny bit. It caused the assembly to shift to the side slightly and the up/down movement of the pawl was crooked which would cause it to not come back down as easily even with the spring's tension. Check your screws and alignment as well.
By the way, all this is AFTER doing the flipper rebuild. It's a good idea to do a rebuild whenever you get a new machine anyway.