Sounds as though you've asked this question before, and didn't get the answer you wanted, so..... here's a brilliant idea!!!
CALL Directed Electronics Inc. The maker of Viper, and ask them WHY you only get .2 of a mile range???
Don't blame it on the shop, blame it on the ignorant advertising of such a thing. How did you decide on buying and having THIS system installed? Did you research it, or did you ask a bunch of internet "friends" for their advice? Did the shop tell you it will definitely work for 1 mile?
Why do you need it to work for 1 mile or even half that distance?
Let me ask this though.... if it did work at a 1 mile range, and your beeper went off telling you there was something wrong, how fast do you think you could get there????
Besides even if it did work for 1 mile, buildings and structures will interfere and lessen the distance.