2009 Four Winds Majestic 28A
Download a copy of owners manual and see what the maker has to say about it.
-Manual describes how to use. And it also comes into play on which maintenance schedule you use.
If you have one of these on a trans cooler line
http://www.magnefinefilters.com/Magnefine-3-8-Magnetic-Inline-Transmission-Filter-R038M.htm?gclid=CKSZ3pP-usYCFUeBfgodoHMN5g trans most likely already has been rebuilt.
RPM noise makes you wonder if your doing the right thing takes some getting used to.
Following the owners manual is best advice IMO. I think I loose about 1/2 per MPG with it on. You probably have a trans gauge. Mine has gone up just a little twice, but still way in green. Both times on Lewiston Hill.