One of my exhaust pipes is working great, the other is hardly moving any air at all. What do I do?

I suggest you use all new exhaust manifold hardware and torque new bolts to 20 Ft Lbs.
4.5L and 4.9L Engines
RIGHT
Disconnect the negative battery cable. Remove the air cleaner. Remove the exhaust crossover pipe. Disconnect the oxygen and coolant temperature sensors. Remove the catalytic converter-to-AIR pipe clip bolt. Remove the upper manifold-to-cylinder head bolts. Raise and safely support the vehicle. Disconnect the converter air pipe bracket from the stud and remove the converter-to-manifold exhaust pipe. Support the engine cradle with screw jacks and remove the rear cradle bolts. Loosen the front cradle bolts and slightly lower the Engine cradle. Remove the remaining exhaust manifold-to-cylinder head bolts, the AIR pipe, and the manifold. Clean the gasket mounting surfaces.
To install:
Install the exhaust manifold and replace the AIR pipe. Tighten the manifold mounting bolts to 16-18 ft. lbs. (21-24 Nm). Install the manifold-to-converter exhaust pipe and replace the converter air pipe bracket to the stud. Raise the Engine cradle and install the rear cradle bolts. Tighten to 75 ft. lbs. (102 Nm). Lower the vehicle. Replace the upper manifold-to-cylinder head bolts. Replace the converter air pipe to AIR pipe clip bolt. Connect the coolant temperature and oxygen sensor connectors. Replace the exhaust crossover pipe. Replace the air cleaner and connect the negative battery cable. Start the Engine and check for leaks.

check for a crack in the manifold to exhaust pipe connection
to allow the engine to move ,there is normally a flexible piece of exhaust pipe in a stainless steel braid that cracks and allows exhaust sound out especially on acceleration
could be even broken at the manifold connection at the flange

It would be great if you could post a picture of the installation and the state you are located in. The sound is sometimes caused when the fuel to air mixture is to lean. If your fresh air pipe is too close to the exhaust it can suck in the exhaust and cause all sorts of problems with combustion. Also, if you are in cold climate and the fresh air pipe is not piped to the outside (on the same wall as the exhaust), you can damage the heat exchanger.

there are many cars that do not have air injection that use cat converters
a cat converter has a very fine honey comb construction made of a special metal that when heated gets red hot and burns off certain gases from the engine combustion process
it does not need extra air

on the air intake is a pipe that picks up hot air from the exhaust manifold ,where this pipe joins the air intake pipe is a vavle which is operated by a bi.metal strip thermostat ,so when its cold it allows vacumn from the engine to open the valve allowing hot air into the intake which stops it from freezing up around the butterfly ,Something is wrong around this area but without having my head under the bonnet i couldnt say ,if your in doubt ask a local mechanic to have a look they will see the problem straight away

It`s probably the exhaust doughnut between the exhaust pipe and the exhaust manifold its a gasket that can move around and be damaged easly

I pumped out water that somehow collected in the exterior exhaust pipe. Even though there is a hood on the outdoor pvc pipe, it still filled with water; not sure how but after extracting the water, the fan works great now.