I finally received the last of the goods needed for me to swap my bike over to SRAM Red. Everything went well. Levers on, derailleurs attached, cables run, bars re-wrapped, cables adjusted so it shifts (front could still use a little tweak). But when I got on the bike for a little test, it skips/pops in the small rear cog. It may do it in the 2nd smallest as well, but it was late and I cleaned everything up with intentions of looking into it tonight.

The cassette and the chain are the same chain (PC-1050) and cassette (Red 11-23) that I was using with my 105 (5700) shifters and derailleurs and there was no problem. Cassette is fairly new, and chain measures OK on the chain gauge.

Any ideas?