Lack of Horsepower

Finding the problem yourself is going to depend on your mechanical skills. Couple of items to check before heading to Ford.

1. Check the air filter. Although your coach is new enough early F53's had a problem with the air filter getting water soaked in heavy rain and restricting air.
2. If you have the tools, check your fuel pressure. The in tank fuel pump could be failing or the fuel filter is clogged. Checking fuel pressure is a lot easier than dropping tank or buying filters that you might not need.
3. Since the V10 uses coil on plug for spark you could have problems with spark but I suspect the ECU would throw a code for a misfire but I might be wrong. Not sure how to test other than buying one wire and swapping to find the problem.
4. Another problem could be with the catalytic convertor clogged restricting exhaust flow but not sure how to tell without removal or replacement.
5. This one is a bit of a log shot but you could have a brake calibrator dragging. Use a none contact IR thermometer to check the disk temps next time you're out. The disk should have about the same temps left to right. Front to back might be different.

Good luck.

I've had 2 V10's. 2005 with 310 Hp and a 2011 with 362Hp. Neither experienced what you described. The 362 was no stronger due to 4-5000 more lbs. Every hill was a challenge. A 5 Star SCT tuner helped about 5-10%.
A diesel with 380 Hp and 3 times the torque was my solution.
What you experienced is very unusual and very hard to find out why. Try running the same route again. Is there different elevations coming and going? Wind conditions? Check gas mileage.

Since you get no codes, I would suspect that you have one or more injectors that have become plugged or possibly O2 sensors that are starting to fail. Perhaps you just got a load of bad gas and it plugged things up or as Dale mentioned, your in tank fuel pump could be on it's last legs.

Sounds like a fuel pump issue.
Easy check and fix by the dealer.

if just bogging down check the coil on plug. You can pull the coil, connect a regular spark plug wire and connect that back to the plug. Take a clamp on timing light and start engine. The flashing light should be the same , if not, low on spark, 9 more to go.

Ford also does it for $$$ per hour.

We had a similar problem in OK after driving thru a torrential rain storm.
Stopped at an RV repair shop and when I explained the symptoms to the tech,
he knew immediately what it was. The filter on our Ford V-10 had collapsed
due to being soaked while driving through rain. New Filter solved the problem

I had a 1999 V-10, sorry to hear about your troubles! It could be water in the fuel from the last place that you filled up.

Based on my loss of power in an 8.1 gasser I would suggest cleaning your MAF.

Which means Mass Air Flow sensor.

It controls the mixture of air and fuel.

About $10 for a spray can of cleaner.