Uh, no.
That rectangular thing is the high pressure pump RESERVOIR. The HPOP is under the fuel filter housing.
To the OP, as has been stated numerous times by those that have a clue, you likely have a fuel supply issue. Have a mechanic install a fuel pressure gauge at the head and road test with the trailer. If the pressure drops even with a new filter, then either the pump is bad or the sock in the fuel tank is plugged. Both are very common problems. You can blow air backwards through the fuel supply line before the pump to temporarily clear debris from the sock. If it road tests normal after this, then you will need to drop the tank and clean the sock or eliminate it. There are plenty of write ups on the web about this procedure.
Also, the PSD trucks will run without the electric pump operating as they have the ability to siphon fuel from the tank. The trucks will often show a lack of power on a long hard pull but will otherwise run pretty much normal. However, once the system is opened, like when replacing the fuel filter, the system will not prime and the truck will run for a few seconds then quit and not restart. The electric motor section of the pump usually works fine, it is the pump section that fails. So, just because you can hear the fuel pump running doesn't mean it is actually producing useable flow. Something to be wary of as you sort this out.
Don't waste time with the CPS, it cannot cause your concern.
Jay