Toyota - Camry :: 2000 - Hard To Change From Lower To Higher Gear?

I have a camry 2000 automatic transmission with 150 K on it. For last few months I am having this sporadic issue with it having difficulty to change the gear from lower to higher gear(from the first to second, i guess). It goes like this, when i start speeding up the car, its having difficulty to move to higher gear, it just revs up to like 5 - 6 K rpm and with a jerk it shifts the gear. And at the same time check engine light goes on. And during the time this check engine light is on, it does this same thing a couple of times or so.

Then after some time the check engine light goes away and the car runs just fine without any issues for some tine and then the same thing happens again and after some time the issue and the check engine light goes away and the car runs just fine again. this keeps happening every few weeks. So I took the car to the mechanic (check engine light has gone away at this time, who told the code was showing some "speed sensor" issue and they replaced this. After that the car ran just fine for a couple of months. But its starting to do the same thing again.