Classic Winnebagos & Vintage RVs

Hello,
I have a 73 D24 Indian on a M400 chassis. Here are some of the various symptoms i am having:

1. Hissing sound when breaks are applied. It appears brakes work but are VERY sensitive. Almost either on or off.
2. Power Stearing leaks from the gear box. Not sure if just needs to be tightened up or what.
4. At higher speeds 60mph there seems to be a whirling sound from right front side. I felt as it was the bearings but they look ok at first inspection. I didnt take the wheel or drum off but took the grease cap off. Wheel does not have play in it. So now thinking the brake is set too tight....?

I have a steep driveway and I do use the lowest gear but still wants to roll pretty fast. Need to get security in not only the main brakes but also an emergency back up. The previous owner said the brakes have been redone but not really sure what that means.

Any advice where to start? 

And the PO said there was nothing wrong with it?..... W%

haha yep. But hey it is in pretty good shape for so old. A lot of work has been done on it. Trying to find a place to take it locally is the challenge. Very few large truck shops around and too big to try to tackle.