Need help batteries, range and general advice

[Dan7man]

Questions on range, batteries, whine - ruff n tuff 4x4
I currently have an 08 Ruff N Tuff Hunter 4x4. It has cheap batteries in it and I get about 5-7 miles per charge (off road and hills). My overall concern is long range of cart. Here are my questions:

1. Was thinking of going to Trojan T875 or Crown CR165 - will they increase my range dramatically (have 2awg wires already)?
2. Could I switch to 8 6V Trojan T105s without any other mods and would that increase my range dramatically (have space for 2 additional batteries under rear seat if I need to)?
3. Would disconnecting the front drive shaft (I haven't had a need for 4 wheel drive and have a winch) harm the motor/cart and would it increase my range (the 4x4 system operates on a single motor)?
4. I have a whine while driving - not in reverse but just in fwd - is that something with the gears/drive or could that be in the motor?

I know alot of people don't have experience with Ruff and Tuff but thought your technical expertise would be beneficial. Thanks!