FloTek will definitely sustain speed runs of 45mph but your biggest issue is trying to mix-match too many terrain types.
For speed runs, you'll want to decrease your ride height, go with stiffer suspension and loosen the center slipper to prevent wheelies, also consider using expo on the...
What are your driving conditions?
Street?
Speed Runs? If so, what speeds?
FloTek will certainly help, but they can only do so much.
In order to mitigate your issues, you can maximize downforce by installing a rear wing or simply do a \BACKSlash conversion: