Fuel pressure

Vacuum should make the pressure go down and unplugging the hose will make it go up. During coasting, intake manifold vacuum is high which tugs harder on the molecules of fuel at the tip of the injectors. To prevent a rich coast-down condition, pressure is dropped so the difference between the two forces acting on the fuel molecules remains constant. If the regulator doesn't respond to changes in vacuum, the higher pressure will cause an excessively rich mixture any time other than moderate to hard acceleration. You might see black smoke from the tail pipe and fuel mileage will decrease.

Your Engine Computer constantly runs tests on the various sensors. To do that it has to compare some to each other. In this case it may be expecting to see a given amount of air flow through the mass air flow sensor based on the position of the throttle position sensor and engine speed. The fault code isn't saying the MAF sensor is defective, just that it doesn't believe the values it's reporting. That would agree with a vacuum leak or leak in the fresh air tube. A vacuum leak will also cause engine speed to increase but under load there will be reduced power. That means you have to press the gas pedal further than normal. That will affect shift timing and harshness. Besides a vacuum leak, the MAF sensor element could be dirty. Bug juice and other dirt insulates it. The sensor works by warming up a heating element, then watching to see how much the air flow cools it. If dirt insulates the sensor, it won't cool enough making it look like less than the actual amount of air is entering the engine. Some sensors, such as on Corvettes, run a very high current through them to burn any dirt off about 20 minutes after the engine is stopped. I don't know if Ford does anything similar, but to be safe, don't spray any cleaner into the sensor for a good hour or two after stopping the engine.

GM has a really huge problem with the pressure regulator leaking fuel into the vacuum hose. I have never seen a defective regulator on a Chrysler product. I have found one split ten cent o-ring that caused a loss of pressure right after the engine was stopped and resulted in a long crank time to get it restarted. I am not aware of any unusual history with Ford regulators. It does sound like the return port is blocked but I think it would be more likely the steel return line to the tank got crushed or the rubber return hose between the engine and body is kinked. 65 pounds seems to be too high and is about the most a good fuel pump can produce. You might consider removing the rubber return hose where it goes to the body, then see if fuel flows from it. If that lets the pressure drop, you'll know the regulator is okay.

Forgot to mention that I never autopsied a failed regulator. It would seem debris that is large enough to plug the outlet port wouldn't be able to make it through the fuel filter. I never heard of cleaning a regulator.

The higher fuel pressure will not cause a shifting problem directly but it will cause a change in the "personality" of the engine. You will be holding the gas pedal in different settings. When the pedal is down further, as in harder acceleration, the transmission will up-shift later and with more force. The clutch packs apply harder and faster to reduce the slippage that takes place until they are fully applied. Under light throttle up-shifts, the clutch pack engagement is softened to give a smoother, more comfortable shift. I don't know how you found the fuel pressure staying too high so quickly but I suspect that is the cause of the change in shifting characteristics. Solve the fuel problem and I'll bet the shifting goes back to normal.

Keep in mind the code isn't saying the MAF sensor is defective, just that the computer isn't happy with the values it's reporting. Here's one possible scenario. Fuel pressure is one of the few things that is not monitored by the computer. High pressure means more fuel will enter the engine each time the injector opens. When the system is working correctly, the fuel mixture switches a few times per second from too rich to too lean. That is detected by the oxygen sensor in the exhaust pipe. When fuel pressure is too high more fuel goes into the engine than what the computer expected. Over time the oxygen sensor reports an average too rich condition. The computer gets confused because the mas air flow sensor says there is the correct amount of air entering the engine. If the rich condition means there isn't enough air to go with the fuel, why doesn't the MAF sensor show that? What the computer doesn't realize is the air flow is normal; it's the extra fuel that it isn't aware of.

I still think you need to reduce fuel pressure. There might be other problems but you could also be looking for a non-existent problem that is a result of too much fuel.