Originally Posted by Benzaah

2 things. When motors unsolder they are gone. Something got very hot to melt the solder and the magnets don't recover. I'd be pulling apart your speedy as well and check the fets and soldering for damage. 4.2 does not sound extreme for gearing on a 13.5.
As for your loose back end. Try adding more front droop so as you have for example 4/4 on the droop blocks front rear vs the kit 5/4. If you are not already try running some anti dive in the front. Go to 1 mm shims under the split blocks in front rear and 0.5mm under the solid front front block. You could also take out some EPA on the transmitter as too much steering throw causes a loose back end on corner exit for me.