If its not straining there is no pressure, could be no connection between motor and pump, or pumphead not spinning, or internal dump valve (if its a Rayvern) bust so oil is just circulating back to tank.
so did they just fit a new motor and not test the whole unit?
(not sure if this is custom or rayvern pump so some bits will differ)
If its not been tested you need to go to the start.............
split the motor from the center block.
drain the oil from the tank.
unbolt the pump head from the center block.
look where any o rings are and remember.
check what ever arrangment there is to connect the motor to the pump.
If thats OK you need to strip the pump head.
probably will be 3 slices bolted together, lots of seals and orings that will probably be directional so check carefully.
You may find that the gear teeth have broken or the shaft has sheared.
post pics as you strip so we can identify.............
