Keep in mind that UHF which includes FRS/GMRS is mostly line of sight. Might push thru some trees, but intervening hills are a show stopper.
That's why serious GMRS uses a tall tower base station.
ht tp://en.wikipedia.org/wiki/General_Mobile_Radio_Service
"...As for other UHF radio services, reliable range is considered to be line-of-sight and the distance to the radio horizon can be estimated based on antenna height. Theoretically, the range between two hand-held units would be about one or two miles (about one and a half to three km); mobile units have higher antennas and a range of around 5 miles (8 km). A GMRS repeater with an antenna that is high above the surrounding terrain can extend the usable range over a wide area – for example, up to a 20-mile radius around the repeater station.[5] Obstructions such as hills and buildings can reduce range. Higher power does not necessarily give a proportional increase in range, although it may improve the reliability of communication at the limits of line-of-sight distance."
VHF otoh can get bounce from the ionosphere, which is helpful when you're battling intervening hills.