[Grounded63]

Is the engine induction method stock ? Like, was this a TBI engine and trans that was swapped. Is it still a TBI. Or was it converted to a carb. And, it may not have the correct throttle arm bracket on the carb. The TV cable needs to travel through a specific arc and range. I would check, confirm this first. Before anything else is done.

When/if you install the 2nd gear servo. Check the actual amount of band engagement. Before you completely disassemble it. You may need to hit the outer cover with a soft mallet to break the seal. Or just remove the retaining clip, pull the cover out enough to remove the o-ring seal. Replace the cover and retaining clip. Then depress the cover, and measure the distance it moves. You'll probably need to find a way. To pry or clamp against the cover to depress it while in the vehicle.

Assuming that the TV cable, throttle arm is correct. I would be look at possibly a sticking/stuck TV piston/plunger ( inside the valve body ). Or same issue with the governor ( accessible outside of the case ).