Hi,
I can't help you with the 88 - 108Mhz frequency range.
But if you would like to go to a much higher frequency 5.8 - 5.9GHz, you could get a much further transmittal distance as well, have a look at.
ADF7025 - Analog Devices
ADF7012 - Analog Devices
ADF4016 - Analog Devices
All used in conjunction with each other. you can transfer baisically any type of data or voice.
You could also have a look at
TRF6900 - Texas Instruments.
still not within the frequency range but worth a look.
you might want to include an FM modulator with the TI chip to lower to those required frequencies.
But i can assure you it will be near impossible to get a 2 - 4 mile range in that frequency range. you would need at least a 50W transmitter, depending on your area as well, there are many factors contributing to the power required.
Regards
David