Agreed, open loop has definitely been working well for me. I set the baseline AFR for all cells at operating temperature to 14.7, and then I use the AFR adder in the cruise cells to run lean. Had to tweak the timing in those cruise cells to work best for the leaner AFR.
Also agree with fivefinger though, you should be getting around 30ish highway to start with. I'd make sure your front O2 is working correctly. I have found they can give totally bogus readings and not necessarily set a code.