Help with Tranny please

[Juck]

Every morning I back out of my garage and onto the street. When I shift from Reverse to D,, there is a delay of about 3 or 4 seconds before the gear engages.

It's only the first shift of the day,,, otherwise the engine and tranny perform beautifully. I checked the fluid level in the tranny and it seems fine. I do not know for sure when the transmission last had a fluid/filter change.

Any ideas what could be causing this? Is this a sign of worse things to come?

Car is a 1993 300CE cabriolet with 90k (head gasket and wiring harness relaced by PO).

Thanks!