leapetrin

Hi! I think I'm having problems with my crankshaft position sensor or my alternator on my 2000 Lexus ES300. The battery has died 3 times. The second time the battery was replaced. When jumped the last time it started immediately. After the battery is charged, the car will work for about 3 months, then suddenly die. When I accelerate the car is jerky and feels like the gas is not 100%, especially after a 4-way stop or going up a hill. The interior lights and dashboard lights flicker when idling and accelerating. Some days the car is fine. When I put gas cleaner in the tank to get water out it seems to run better for a bit. Is this a possible DIY repair? I have already ordered the part. Might it be an alternator problem?