High fuel pressure?

The fuel pressure regulator is supposed to provide a pressure drop in the fuel line at idle. Either the ECM is not receiving the indication the engine is at idle (off throttle) or the regulator is not working. It is not the fuel pump!

It could be:

1. A bad hose attached to the intake manifold.

2. Stuck PCV valve (related to item 1)

3. A failed MAP sensor (Manifold pressure sensor)

4. A failed fuel pressure regulator

There might be others, I just can't think of them right now.

With this being a ten year old vehicle, I would start by checking all the hoses that are attached to the intake manifold. There are instructions on how to test the sensors for voltage and continuity on line.

LOL! You are using the WRONG OIL TYPE< like VALVOLINE instead of REAL SYNTHETIC OIL  that is REQUIRED on most engines these day! VALVOLNE is NOT used by ANY FACTORY on EARTH for GOOD REASONS! It eats up RUBBER PARTS and causes seal and gasket leaks and DIMINISHED crank venting over time as hoses ROT and TARRY coating begin to accumulate inside! >>>>ANYWAY CHEAP FIX HERE! get a can of AMSOIL POWER FOAM from ONLINE or AMSOIL dealer! REMOVE the IDLE AIR CONTROL VALVE using an 8mm wrench or socket! Using the AMOIL< the FOAM will expand and force out YEARS of sludge And TARRY buildups and it will WORK AGAIN! CLEAN the THROTTLE BODY as well and run the AMSOIL POWER FOAM through your PCV valve to clean the piston rings and valve heads to SHOWROOM conditions!  You do NOT have a FAILNG FUEL PUMP here! Use ONLY TOP TIER fuel to PROTECT the pump from METHANOL FAILURE! >>once you get the IDLE AIR CONTROL VALVE and throttle body CLEAN on BOTH sides of the throttle plate and runt he AMSOIL through the PCV< all things will return to NORMAL.>>>begin  using PENNZOIL ULTRA EURO or ULTRA PLAYINUM with "0" series, Like 0W-30 or 0W-20! This protects down to 35 below ZERO! It gives you an AMAZING extended engine warranty to 500,000 miles as it is NOT made from CRUDE OIL but from NATURAL GAS! IT CLEANS as you drive and PROTECTS pricey engine sensors from SLUDGE and TAR and WAX and VARNISH!  >>> once your IDLE AIR CONTROL VALVE is CLEAN or REPLACED< the idle will return to NORMAL! Using the PENNZOIL SYNTHETIC HERE will PREVENT other issues from pooping out and you will FEEL the engine running BETTER as the old baked in MUCK Y OIL is removed from the PISTON RINGS< the OIL PUMP< the VALVE COVERS the BREATHERS and EVERYWHER in between!  NEVER USE VALVOLINE. an oil NO FACTORY on earth will use due to it's affinity for making SLUDGE< TAR< WA< VARNISH and other deposits! I also like AMSOIL, LIQUI MOLY, TOTAL ENERGY OIL, and MOTUL! STAY WAY from cheap oil change bargain specials! They use CHEAPER OIL usually and PAPER filter elements! Nearly ALL engines in junk yards got there from the OIL CHOICES used! I HAVE SUED And OWN over bad OIL CHNGE CENTER OIL USE and ENGEIN DAMAGES! Also sued CASTROL< CADDY, JEEP, GM many times! Run the AMSOIL POWER FOAM through the PCV VALVE< and if this engine can use DENSO TWIN TIP IRIDIUM SPARK PLUGS< use them! Many FORD heads require a SPECIAL TYPE OF PLUG and special TOOL to remove the plugs or the heads will need to be removed and RETHREADED! SO BE CAREFUL! HAVE a shop install them for you if DENSO makes them! These pugs will get MORE POWER< LOWER EMISISONS and improve drivability and mileage! BEST THINGS ever invented for CAR ENGINES! CHANGE the PENNZOI once or twice a year and LEARN how to READ YOUR OIL condition on the DIPSTICK! SO many change their OIL too soon and WASTE MONEY and the environment as well! N= MODERN SYNTHETIC OIL can be good up to 25,000 MILES (AMSOIL) WALMART carries PENNZOIL At most locations. Use the "0" series oil good to 35 below zero! LIKE oW-30 or 0W-20 etc! ALSO ADVANCE carries these oils as well! ONLY PENNZOIL gives a 500,000 mile ENGINE WARRANTY with proof of purchase! The oil is made from NATURAL GAS and NOT crude oil! It SAVES the planet, and will SAVE your pricey CONVERTER and O2 sensors as well! AND prevent MANY sensors from failing! GOOD LUCK! The engien getsd CLEANED every time and DENSO IRIDIUM PLUGS will burn MROE fuel MORE completely as it REACTS at the molecular level! I got #@ MPG from an old BENZ C280! EXPECT 500,000 miels and GO FROM THERE! But iit is ALL ABOUT your OIL CHOICES NOW! and NEVER use PRESTONE EITHER! Use ONLY GENUNIE FORD COOLANTS and other fluids as well! BYE NOW!

Even if it hasn't lit up your check engine light the PCM module might be throwing some codes, so take it to a local parts store and have them run a quick free scan unless you can do it yourself.

Access the level of maintenance you've done with the truck, the 3 valve engines have a number of issues tied to oil change frequency (or lack there-of). The first thing is to check codes, look for Bank 1 or 2 issues, that could lead to a common issue of plugged V V T solenoid(s). A plugged solenoid will give you the issues described, often even a "dieseling" noise. The solenoid(s) alters the cam settings at various speeds/RPMs. The unplugged/default mode is non-advanced, so it will idle smoother after coming to a stop than when at cruising speeds, and there are videos to help diagnose this and the other 3 valve issues. Below is one example video: 

https://www.youtube.com/watch?v=itI9uysEp4A&ab_cha...