This weekend saw some bad storms come through so I took the downtime to do a much needed tuneup on my bike. Took off the chain and did a scrub and clean on it, the crank and the cassette. I was having some mild skipping and jumping problems before the cleaning. Now what is happening is that when I shift from lower (bigger) to higher (smaller) it ships from 6 right to 8 (8 speed cassette). If I shift from 8 back to 7 it stays there and doesn't skip out. Only coming down the cassette.

Does this seen like a cable tension problem? If I adjust the barrel a few clicks either direction it seems to mess up all the other working gears.

Old 99 Diamondback, low end components all the way around, RD is a Shimano 8515. Aside from all the low end stuff this thing had been bomb proof.