You say he has no downshift going uphill. Will the car downshift if he manually shifts from D1 to D2 (not Lo)?
'56 Cad. P-N-D-D2-Lo-R I assume his Chevy is the same? Maybe without P.
I also notice that the transmission is a hybrid of 1954 and 1956 Hydramatics. Depending on the '56 parts used, that might be the source of his trouble. The '54 and '56 Hydramatics are not interchangeable even if some parts look identical.
My '56 Cadillac transmission had a Pontiac valve body and was never able to be dialed in properly by the book. Obtaining the correct '56 parts for the '56 transmission solved all my issues.
Last edited by Otto Skorzeny; 07/29/2022 6:56 PM.