Runs better prior to drive cycle

2000, Ford Windstar, 3.8 liter.

For some strange reason, when I reset the PCM by disconnecting the battery for about 10 minutes, the van seems to have better power and smoother shifting. A few days later, after completion of the drive cycle, it seems to lose a little power and not shift as smooth. No codes being thrown before or after drive cycle. Any ideas???

Well when you disconnect the battery you are in fact removing the "learned" values. This means that the PCM uses a factory default for these values until it re-aquires this data.

From what you describe it sounds like the "learned" data is making it run rough. Perhaps they are not good values based on bad input perhaps a bit in memory is stuck and the PCM reads somrth9ng diffrent then it stored.

I would be suspicious of an O2 sensor that is not healthy, they can be quite off and not set any codes