Regarding PMDC motor attached to gear box
It is hard to be sure because the nature of the load is not really known. Seems like it is mostly friction that is causing your load. The friction may not be constant with speed. But since we don't know, we will just pretend that is true. So then I guess I would start by changing the gearbox ratio by the same ratio as the currents. 7A/3A = 2.3. So You want to multiply your gear ratio by 2.3. My gut tells me that this is not quite right. Slowing the array will also reduce friction. So if you make the change, you may end up with even less than 3A.

A lot of guesses on my part. It would be much better to have real data, like the torque constant for the motor, and the torque required to move the load at different speeds. Then I wouldn't have to guess.

Another thing to keep in mind is that the torque required to move the array may change over time due to corrosion or dirt getting in the mechanism. This may cause the current to go up later.

You asked about the gearbox. But if it is easier, you could also just use motor control to slow down the motor. That should also reduce the current. If the motor controller is built-in to the motor, which it sounds like it might be, you may be able to reduce current by just reducing voltage to the motor controller. Read the documentation for the motor.