I owne a 07 GS 8389 40' Diesel FRED. I love the unit. The only problems I have had with it is the reverse lights did not work when purchased. ( check them ) and the fridge is on a slide and it did not work properly due to the mis installation of the temperature sensor on the unit. Other than that enjoy. I have not noticed the dragging on dips yet and have had mine in some pretty hectic situations. I use mine to pull a 16' enclosed trailer loaded with dirt bikes. I usually end up parking it in some cow field to attend the series races. Have only been stuck twice in the last year. They roll great on the pavement but slip and slide on wet field grass
The coach you have is built a little different then most other gasoline coaches. I believe your FRED is built on a Freightliner chassis rather then the usual F53 or workhorse chassis.
I used to have a gasoline coach on a F-53 chassis and it was 36' long. Everytime I hit a dip it would drag. Finally I discovered that it had Firestone air bags out of the factory, so I inquired about how much air those bags had to have, since they never told me anything about them when I bought the coach. They told me to put 90lbs of air on each side. It raised that rear end right away to where I didn't have the dragging problem anymore. Freightliner chassis are heavy duty.
I have the Freightliner Neway on my diesel pusher and it rides real nice.