Need more to go on... Assuming there isn't something wrong with the car from the installation of the new parts.

The time slips from the before and after, and also how many runs. If the car has much more power from being modified it could be all traction related, even with the slicks. What size are the slicks, are they taller and you lost gear? How experienced of a driver are you at the track?

The MPH is rather low no matter what, which does point to me something is amiss with the car.