Marty,
In The 1941 - 1948 Chrysler Service Manual, Page 143, there is a Cut Away Carburetor Picture of the Kickdown Piston inside your Carb that isn't sending the message to kickdown your Transmission at your Governor. It is either clogged or your Points on your Governor are, or something is amiss with your wiring. The Carburetor Solution I am suggesting costs nothing but a gasket and an hours work. You do not even need to open the Top of the Carburetor (Air Horn) to Service the part I am suggesting.
I was checking, testing, replacing parts, cleaning Governor Points etc., etc. until I did what I am suggesting to you my problem (Identical to yours) persisted.
I even had previously replaced my entire Engine Wiring Harness. I spent close to a thousand Dollars to sort out my problem - namely a clogged Kick Down Piston in my Carburetor. Good Luck with your solution. Please post us what you did to find yours, I typically don't post a lot on here anymore so consider yourself lucky to get this information because sorting out my Transmission Glitch was a MFSOB to put it lightly. Also change your 30 Amp. Fuse at your Transmission Solenoid.
Best of Luck to you. (The Wire from that Part of the Carb to the Governor is Yellow)
Tom