1997 Winnabego Brave with chevy 454

I am having a problem and have spent several $1000`s of dollars and no one can figure it out I even had to tow it 200 miles home I have a 31 foot brave with a chevy 454 in it problem is I was on a trip 680 miles into it with no problems stopped in Indiana got gas and then it started it ran fine then lost all power slowing me down to 10-15 mph changed the fuel filter and mass air flow sensor it idles great starts right up you don`t even have to step on the gas pedal rev it up does great put it in gear and your done it spits and spudders and chokes you out with the rich smelling fumes you can not go over 10-15 mph anyone else ever had this problem or no what can be the problem I only have 34,000 miles on the rv thanks for any help I am ready to get back to rv`ing