The only way to change the gear ratio would be to build a different set of planetary gears, something that's not very likely. There might be somewhat different spring tension on the shift valves, but the most likely difference would be in the calibration of the modulator and/or governor calibrating springs. Non-computerized automatic transmissions shift by balancing throttle pressure with governor pressure and allowing the shift valves to move. Throttle pressure is controlled by either mechanical linkage to the engine, or manifold vacuum applied to the modulator. Governor pressure is regulated by driveshaft speed, moving a spring-loaded valve geared to the output shaft. Since the diesel engine has no manifold vacuum, the modulator on the transmission is supplied with vacuum from an engine-mounted pump, which also generates vacuum for the brake booster, and the vacuum is metered through a mechanical valve moved by the throttle linkage.
Most modulators are adjustable, either with a setscrew and locknut on the factory-original units, or a screw inside the vacuum nipple on aftermarket replacements. Turning the screw clockwise delays the shift, while CCW adjustment makes shifts sooner, and softer. Most aftermarket adjustable modulators can be changed a maximum of 3 turns in either direction.
Stay away from shift kits! They tear up rear ends! Also, the transmission bolted to the diesel engine will not fit a Chevy engine, since the diesels have the Buick/Olds/Pontiac/Cadillac bellhousing bolt pattern. Adapter plates are available, however, and some transmissions will have dual-pattern bellhousing bolt holes.
Jerry
