I do all my own bike work. I get parts cheap too, from -- Bicycles, Bike parts, Mountain Bikes, BMX, Road Bikes, Haro Bikes, KHS Bikes, Felt Bikes at Niagara Cycle Works
, nashbar, and sometimes a few others like e bikestop.
I don't understand why people (usually pedal bicyclist) want to shift under power. This causes so much more cassette and chain wear. Easing up just a little bit on the pedals (or the gas in your case) will let the chain just fall swiftly into the next gear without the hard CLUNK or worn or broken teeth.
Steel cassette gears will do much better, and a chain checker or metal ruler are essentials for keeping your drivetrain in check. Steel freewheels are still a good deal for heavy use, and can be had in the 34,28-13 varieties called "MegaRange".