Car rental companies generally don't guarantee specific models. Even if you select like a convertible Mustang, odds are they won't actually have it. They'll give you something that "meets or exceeds your reservation", like a chevy suburban.
Turo is much better if you need a specific vehicle. In Alaska, Hawaii, and Utah I've rented 4WD vehicles when I needed 4WD. They almost all still say in the contract that you're not allowed to take it off road. I always contact the renter ahead of time to make sure it's okay if I go on dirt mountain roads that need 4WD and I've always found someone who approves. I'd guess you can get what you want on Turo.