2000 Toyota Tacoma temp guage

When I'm accelerating, my temp guage goes up dramatically, but when I let off the accelerator, it drops back quite a bit. Also, occasionally when I turn the engine off, the temp guage will go all the way to the top. It should drop to the bottom. If I leave it this way for a few hours, the battery ends up drained. After I either charge or jump the battery, it takes 8-10 times before I can get the engine to start. It cranks fine, but just won't kick. Once I do get it started, it runs fine. I thought it was maybe a head gasket filling a cylinder with coolant, but I haven't lost any coolant. Could a faulty temp sensor or guage cause these problems, or could it be the ecm.