The OEM sensors (with probes that go into the tank and typically a four light panel somewhere) are temperamental because of the probes becoming fouled up with, erm, debris. Flushing out the tank with a flusher or a wand you put down through the toilet will help, at least for a time. Not being skimpy on flush water quantities can also help a tiny bit, and is generally a good idea anyhow. Experience will often suffice for knowing about how long you can go before having to empty the tank.
Pulling the tank to fix this is in my opinion pointless. Capacitive sensors (such as SeeLevel) are somewhat more reliable, and installing them generally should not involve actually removing the tank--nor, for that matter, would working on the probe kind in most cases. All you need is some access to the side of the tank where the sensors are, often also the side where the drain pipe and gate valve are connected.
