This unit achieves the same airflow vs. energy used from either side or the bottom. It cannot pull from the back of the cabinet. Both sides of the housing pull equally even though the motor is on the right side facing.
I would be led more towards undersized duct..either supply or return...or potential plugg ac coil, if equipped.
You can see here the installation instructions per manufacturer.
There is no gain by reversing the blower motor...
However....many contractors do not cut the entire allotted space from the side of the furnace.
You may want to have an hvac tech check the system for duct static and balance.
I will say though I have had issue with the energy inspectors not knowing the whole picture.
Example: Here the concern is the draw of the motor....what if I cut an extra return in the other side of the furnace and an extra supply in the top? The motor will now run comfortably...but I have done nothing to use that saved energy to heat/cool home and have actually impeded the system by short cycling the air in and out of the furnace without using duct.
You could gain maximum motor return by unhooking all the duct...but in turn the unit runs longer because of impeded delivery.
My point is...make sure the issue is worth investigating, and then that improvement does not cost efficiency elsewhere.