Slack chain in lower gears
 

Ok, I have not measured chain wear, and think that MIGHT be the issue, but how loose/slack should the the chain be if I am on my inner ring (double, 38) and I am on the bottom couple of gears on my cassette (12-27)

The chain skips a bit and pulls the RD up if I am in the bottom two gears while on the inner ring and it is extremely slack. Is this a chain problem?

The problem does not occur when I am on my big ring up front (53)

What else would you guys need to know?

There is no way chain wear is going to cause a properly length to chain to not be proper length in any meaningful way.

Do this procedure and find out if it is the right length to begin with. http://sheldonbrown.com/derailer-adjustment.html#chain

Don't stop there on Sheldon's site. Also check into chainline and cog wear. You cannot find a combo that will wear a chain and cogs more than the small-small combo, due to the small number of teeth engaged. On most bikes a combo with the larger ring and larger cog will yield the near the same gear ratio.

Ok thanks. I will try that this week when I get a chance. Just don't want to ruin my RD or anything. But it seems that for right now, just avoid the small-small combos, and I am ok.

I generally don't use the small-small much, but have when riding on "2 gear" days. Just setting the rear gear and then only changing from the big or small ring in front.

Otherwise I will go to the larger combo.

Maybe your chain's too long, and the rear derailleur can't take up all the chain slack when you're in the small ring/smallest cogs. Measure your chain length, it needs to be capable of covering the large chainring/large cog combo, but it doesn't need to be longer than that.........Your chain shouldn't be slack, one of the two primary functions of your rear derailleur is to take up all the chain slack no matter what gear combo you're in-