LOL, the last of my youth went out with my 41 Chevvy High school car.
I hate to alarm you, but if you needed three quarts of Trans. Fluid, and no obvious leaks, your vacuam shift modulator is leaking, and your engine is burning the Trans. Oil.
Either that, or you better have one of the Kids do your looking for leaks!
Here's a link to trouble codes. It tells you how to read the codes out, and what they mean.