temperature is fluctuating but not overheating.

2004 chevy impala, temp runs up to midway point then comes down to 1/2 way between 1/4 and 1/2. which i assume is ok. but it never ran that warm before. looked for leaks, put cardboard under car and found a spot the next morning under water pump area. replace the pvc elbows in the block which were corroded. still the same, and i seem to have to add antifreeze everyday. replaced the water pump and thermostat, fans seem to work ok. a mechanic looked around the engine and didn't think head gasket, no water in oil. i quess my question is where should that temp needle run at and what is the midway point in degrees? and also the upper hose can get extremely hot and feel like pressure in it while the bottom hose stays cooler. the pressure in upper hose goes away and the hose cools down. wondering if am i chasing nothing or is something actually wrong? i don't remember it running that warm before, again i don't believe it over heats just hotter than i remember. and can the temp sensor become lazy? any and all thoughts appreciated.