If the 2001 came from the factory on 29's (A lot did for example), a 35 would be ~ 20% more in diameter.
Going from a 4.6 to a 5.15 is only a ~ 12% increase.
If you mean from a 32 to a 35, that's ~ a 9% increase.
So, if you want to get back to FACTORY gearing, you'd need ~ 20% lower gears for the diffs, and if you want to get back to what its like on 32's, ~ 9%, etc.
As mentioned by Granite, the larger tires have MUCH higher rolling resistance, so, you need more torque just to compensate for how much harder it is to roll the tires.
The lower the gearing, especially off road...the higher your RPM can be in any given gear. The rpm is typically too low to have enough engine torque if the tires are too tall for the gearing.
The lower t-case gears, such as Casper is selling right now, would really help with that off road at least.