Temp gauge drops when engine is revved!!!

I have a 96 tacoma, 2.7, 4x4, 5 speed.
My truck broke down and had a check engine code of p0115 (engine coolant temperature sensor malfunction). I replaced the sensor with a new one, it started but still had problems running, so I drove it around a couple of miles to let the ecu "learn" the new part. It drove great for about a week and a half or 150 miles, then on last Saturday it would not start so I had to call for a ride into work. When I got home from work it started and ran fine. Today I got ready to leave for work and all it would do is turn over,I had to call for a ride. I got home It started but I had to rev it up to get it to run. I thought that maybe It needs to relearn the part again so I let the truck get up to temp and revved and saw the temp gauge drop. It is showing the same code as before. So should I try to replace the sensor again, or try some thing else. Please help!!!!!!!!