Did you get the new blend motors calibrated after you had them fitted?? Were they a new or used set ??
Diagnostics can also "Force" the individual motors throughout the range of travel to check the function.
Did you splice the cables on the motors into the old loom from the HEVAC or fit the motor loom complete ? If you spliced the cables, you could have a bad connection somewhere, maybe at the splice or the HEVAC socket. Last area could be a faulty HEVAC.