Idle Rpm High in Park, Low in Drive

Mattax,
Are you able to read? My comments about Chrysler & MVA was that they didn't get it wrong very often but they did with MVA. That is NOT a criticism of everything Chr, just one thing. Hardly a 'crusade' criticising one thing. All manufacturers make mistakes. For the record, in my opinion, out of the big three, Chry was the best & got it right the first time more than the other two.
And apparently you forgot, or didn't know, that Chrys used MVA "When coolant temps at idle reach 225, the valve opens automatically & applies manifold vacuum directly to the dist....This increases engine idle speed".

And your nonsense about load on the engine & losing rpm. If you drive up a long hill [ load ] your rpm will drop UNLESS you increase throttle opening to produce more power & keep rpm up. Get it now?

I provided one possible reason for the magnitude of the OPs rpm drop going into gear. That scenario is veeeeery common & the usual cause that I have seen in 30+ yrs of tuning. Since the OP provided no timing #s, all I could do was take a guess in this case. Other possibilities would be a very lean idle mixture &/or the centri weights were activated in Park, but then dropped back when placed in gear, reducing timing in gear.