you need to check for an intake leak. my car did almost exacly the same things. in open loop it ran fine. closed loop it would bog like crazy and missfire on 2 or 3 cylinders under a load such as going up hill or taking off at a light, as soon as the rpm's were above about 2500 it would clear up. try spraying starter fluid or some other combustible like carb cleaner around your throttle body and vacuum hoses and if your rpm's go up, there's your problem. this may not be your problem, but it's quick and easy to check.