[Fairtax4me]

Yeah the problem is Amps = Torque. And You need Torque to turn big tires.
You can make some incremental upgrades. Alltrax does make an XCT controller that will plug into the Regen2 harness.
The reason I say to upgrade the wire harness to an IQ harness is there are some issues with the Regen2 harnesses that can cause problems. It’s also more complicated to upgrade the throttle control. The pie-wedge V-glide throttle will work, but it’s a multi-step pot and you will always have some jerkiness in the throttle response because of that. Some can be tweaked out with settings in the alltrax, but it will ever be as smooth as the MCOR continuously variable pot throttle used by the IQ system.

An Alltrax controller upgrade will give you some extra power going up hills and open up the speed a bit.
The stock motor is still very limited power wise, and is not going to be happy for long trying to push those big tires around. You can get by with it for a while by tuning down the output of the XCT controller, but the stock motor can only do so much.
One other option would be to step down in tire size. A 20” tire will make a noticeable difference in climbing power. You’ll lose a few mph on the top speed, but if there are a lot of hills in your area it will be much better off to be able to climb.

Something else to consider is the shape the batteries are in. How old are they? How much does their voltage drop when under load? An older battery pack that’s lost some of its capacity will have a higher voltage loss when put under load, and that means decreased power.

I’m far from an expert on these sort of upgrades, but if you want to be able to turn 23” tires on hilly terrain, you’ll never be happy until the entire drive system is upgraded.
For better advice on what you can do now, and what you can do to plan for future upgrades, Get in touch with ScottyB at CartsUnlimited.
Or David at Revolution Golf Cars.
Both of those guys are experts and will know the best approach to get you the performance you want.