Shifting to park drops RPMs

Test driving 95 Windstar after front cover gasket replacement and when shifting transmission into Park, the rpm will drop to around 400 and then rise back up to what seems it's normal idleing speed. Other then that the van seems to run pretty well. I'm the guy who removed and replaced the front cover with the cam pos sensor attached.
Does this sound like a timing issue?

I would think that you would see other problems if it were a timing issue.
Shifting into park or neutral removes the load of the transmission from the engine......so it may be the PCM trying to adjust to the change in load.
If this is the only problem you are having......WAIT a while......as....if you had the battery disconnected during the repair process.....it will take the PCM some time to relearn the "drivability" information. During this time, you may see some idle, and shift point issues. It does not take long for the PCM to relearn the information.
If the problem persists, then you might try cleaning the IAC (Idle Air Control) valve....as it is a possible symptom of a sticking IAC.....but, again....let the PCM relearn the information over the next several days.

Thanks Wiswind, patience is a virtue.