Turbo 400 trans issue

I have th400 I just put in the truck and it won’t go into reverse (at all) and can’t feel a bump or anything ,it actually goes forward(drive).but stays in one gear .would a bad governor or modular cause no reverse ?
Pull off gov. Cover and pull out gov. Hold it by the gear and move the weights in and out to see if valve moves freely if not that could be your problem depends on where it stuck if that doesn't fix it you going to have to pull the pan and check for sticky valves in valve body. if the valve is sticking you can pull the gear off the end remove theroll pin take out the gear you can pry the valve out with a screwdriver clean it with some solvent check it for trash or bur on valve reinstall
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