[buttnekked]

I just bought a 99 and with 265 tires I get about 14 in town and 17 on highway. The 5.3 has great power and yes mine has most of the typical silverado issues. The gas gauge is the most annoying.
The smaller trucks are a very good budget idea but they won't be noticably bigger than a typical 4 door civic inside. My main suggestion for you considering your age would be to check with your insurance for quotes for coverage on the different trucks you consider. As I remember at 18 insurance was way more expensive than gas. Whatevre you decide; enjoy it.