Engine/transmission hesitant and sluggish

I had my Taco parked for two days with almost no gas in the tank (1/8). When I started it again was slightly in a rougher mood, but not much. Getting out of my block needs like a minute of stop and go, slow driving.

After that I got on the big flat road and trying to go faster was not so easy, felt a bit sluggish. Driving around 50-60km/h the car was vibrating quite strong, and the rpm was around 1000 or less, which is completely unusual, and the transmission wouldn't downshift. At around 80km/h the rpm was 1500 and not much vibration.

The vibration was obviously from wrong gear and not enough power. And no, I know that you'll say, that is normal behaviour of an auto tranny in Tacoma, but this was waaaaay worse and for waaay too long distance. I had to slam the accelerator way harder to make it downshift, and still would feel sluggish.

That evening I went and filled up. For three years I had the car I learned that fuel gauge is very accurate, so I estimated to fill up 62-63 litters, but to my surprise I could get in only 59.

Is less than a week since the problem started. The problem is still there. Idling is fine, constant at 600rpm, like always. Overall the car feels sluggish. The key point is the moment of downshifting. The feel is the engine is almost dying before downshift. Is like the engine has to blackmail the tranny to downshift. Again, I owned this car for three years since new, is 2012 model, V6, auto (A750F), but this is not the regular stuff the car is pulling to save gas.

Anyone, anything? Foul play is a possibility, maybe somebody put something in the tank overnight. Can be fuel pump? MAF sensor dirty? I’m dying here like my engine...

 

Just an idea, but a bad spark plug(s) will cause what you're describing.

 

That would be good news because next service I have to change them anyway. Still I don't really get why the problem started suddenly and not gradually...