First, WELCOME!!!
Next, I doubt much is actually wrong with your coach. More to follow...
Please post the Make, Year, Model and Engine Size of your Chassis. Go by the CHASSIS manufacturer's label in the driver's door jamb. Your coach could be a 1994 per coach builder, and should be registered that way, even if (say Ford's) Label says 1993 and the VIN comes back as 1993. Many "Year X" coaches are on "Year X-1" chassis.
My thought on the Loss of Power issue is that there's a blockage in the exhaust.
First, Listen at the end of the tailpipe. You should hear the beat of exhaust pulses. If you hear a hiss or a wheeze, suspect blockage and work your way the full length of the exhaust system.
While you're at the rear, look into the tailpipe end. If there's a Screen there, it's likely to be covered in rust flakes that originated in muffler (maybe pipes, probably muffler) and are now blocking the escape of exhaust.
Now examine the whole run of piping. Look for dented/collapsed areas.
The Muffler. Try to shake it and listen for a sand/gravel sound inside. Might be full of rust flakes.
Catalytic Converter. Ford uses a one-piece block of catalyst. With engine COLD, get under there and try to shake it. If you hear clunking, that block (monolithic catalyst) has broken and pieces could be blocking the exit.
Forward of Converter. Continue all the way to the Engine and make sure the Crossover Pipe isn't bent badly or crushed.
I have seen, and fixed Collapsed Converter Monolith, Bent Crossover, Clogged Muffler, and Clogged Tailpipe Screen. In every case, very short on power, and if you kick it into downshift, RPM's rise but Power goes DOWN.
I want your Chassis Year and Engine to try and look up the Belts. For awhile Ford left multiple Vee belts behind but kept one along with the newer Serpentine type. Sounds like what you have. For years, they've had only one, Serpentine, belt.
May sound strange, but on a much older Ford-based Class C we had, all Vee belts, the "bargain belts" would work on the Power Steering/Water Pump drive, but the A/C drive and the Alternator drive HAD to be premium ones. Gates, Dayco, Goodyear, Motorcraft, NAPA. They'd last for years. Cheapies maybe 200 miles!
