My Hydra-Matic shifted very poorly when I bought it. The fellow who had owned the truck for many years had tuned it "by ear".
The shifting-points and down-shifting (foot pedal to the floor) are extremely sensitive to carburetor adjustments. I followed the adjustment procedures in the
1954 Chevrolet Truck Shop Manual (similar procedures are found in the 1953/54 GMC Maintenance Manual) and it now shifts smoothly and at better speed intervals. It also now down-shifts in a very smooth manner (it's got some "scoot" and impresses my friends).
This 1954 Hydra-Matic Maintenance & Adjustments Manual is also quite helpful (thank you, Greg Hill & Keith Hardy).
The 53-54 1/2 ton GMC Hydra-Matic is quite similar to the 1954 Chevrolet 1/2 ton truck Hydra-Matic.
