OK, before my ambien really begins to kick my ass (I can say ass) here's how you tune your RD. Assuming it really truely needs it. Shift into your highest gear (large chainring, small cog). Is your RD cable loose? Fine. Loosen the bolt that holds the cable. Check your high limit screw, the pulley should be directly below the smallest cog (the one you put your chain on). If it's to the outside of the cog, turn the High limit screw clockwise slowly until the pulley is directly below the cog. This will be the same at the other end of the cassette. Now, take the barrel adjuster on your RD and turn it in all the way. Done? Good, now back it out 2 full turns. Stop touching that. Pull the slack out of the cable, pull it kinda tight. Tighten that bolt so the cable can't slip back thru. Go thru your gears. Check the limit screw at the low end, make sure the pulley is directly below the largest cog. If the pulley is to the outside of the cog either fix it or start saving for a new rearwheel, chain, RD.