Guessing your '99 vacationer is a Ford F53 chassis, seems this vital fact was not mentioned.
Do you have a check engine light?
And if you do can you find someone who will plug a code scanner into it?
Same ODB2 scanner as any modern car, any Autozone will do it.
You need to start with new spark plugs. V10's get bad coils, but those will throw a code and can be tested, don't want to replace them willy nilly.
As for not fixing things that aren't broke, I agree but... now that something is broke, it is time to catch up on the deferred maintenance