I will agree with Jeff to a point, the pre amplifiers only job is to compensate for line loss.
On 88 - 108 MHz there is not a lot of loss - hence there is not a lot to be gained by using a preamplifier.
Winegard maintains a web site which can be accessed via internet - what you need is a antenna with better rejection and more forward gain.

Because you did not post a physical address, there is no way for sure for me to give you accurate information - because my crystal ball is broken...

Go to FM Fool.com and post your address and you will get a beam heading and distance to the transmitters.
It will also show a graph with what is between the transmit and the receive antenna's...

FM works on the principal of capture effect - hence it will receive the strongest signals and reject all others.
Your problem might be that you have another station on the same frequency or close by that is stronger then the signal you desire...

The Winegard 7694 - 7698P antenna's are a very good source for better reception. You might also want to incorporate a good antenna rotor...