In order to get around the psi problem, fill your fresh water tank and let the on-board water pump do the work. Your water pump is probably set at 55 psi (pretty much the standard), and should operate the ice maker as expected.
Also, if you fill your water tank and then shut off shore water or disconnect the garden hose, you NEVER have to worry about high or low water pressure, campground water pressure, or anything. If the campground water pressure is excessively high, then fill the fresh water tank slower. That's all you have to do. Of course, running the water pump does result in the pump making noise. But the decision is yours, noise or inferior ice?
Ever since our first outing with our first travel trailer, I've never run water directly from the garden hose. I've always filled my fresh water tank. As a side benefit, if there is ever a water leak, or a faucet not shut, or a leaking toilet, the water pump will kick on after only about 3 ounces of water are released. You'll hear the pump running and know water is going somewhere..... hopefully ... not all over your floor! Because you hear the water pump kick on and off, you know water is running somewhere. You can now simply turn the pump off and figure out where the water is running. If you are hooked up to city water / water spigot, you could run a thousand gallons of water through your trailer and never know you have a water line break because there is no noise.
If you've ever had a water line anywhere in your camper come apart or begin leaking, you'll know what I'm talking about!