Accelerates/passes very slowly as trans refuses to downshift when in Drive.

this is normal for the trans to downshift as the engine and trans are working together to handle the acceleration of your car and as your car's speed increases the trans will adjust again (EG: shift gears) this is more of a weight to acceleration sort of thing or rather weight to power sort of thing

try briefly lifting your foot off the pedal, then punching it to get it to downshift.

Hello
The Engine and Automatic Transmission (not applicable to manual transmissions) in this vehicles drive train are fully electronically controlled by a computer called the PCM and TCM (Power Train Control Module, Transmission Control Module). When a problem like this or other drive-ability related problems occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump, engine coolant temperature sensor and MAF sensor for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL A TRAINED TECHNICAIN HAS DIAGNOSED THE PROBLEM TO AVOID SPENDING YOUR HARD EARNED MONEY ON PARTS THAT MAY NOT CORRECT THE PROBLEM. Also always check fuel pressure for correct spec for your make and engine type.

Since you changed the sensor we will assume it is working. When you disconnect it you put the computer in limp mode which stops it from using sensor values. If code 300 is the only code we will assume the coolant temp sensor and others are ok.
I would check fuel pressure with a gauge next.

Hello
The engine and transmission in this cars drive train are fully electronically controlled by a computer called the PCM (Power Train Control Module). Whenever a problem like this occurs the computer stores a record of the problem (there are of course some exceptions to this, like the fuel pump, engine coolant teperature sensor and MAF sensor for instance) in the form of a fault code in its memory, to read these fault codes you must have the systems memory scanned with a special tool. Once the fault code(s) are read you then must perform the appropriate diagnostic testing to find and resolve the problem(s) DO NOT REPLACE ANY PARTS UNTIL THE DIAGNOSIS & TESTING IS COMPLETED.

i could be wrong here but sounds like the toque converter when locked up don't want to let go when you hit the brake or downshift.it can be a solenoid or a control valve sticking.you can either try changing filter and fluid are try adding some lucas trans oil to it at the local auto store.

I think rebuild try and service it if you find any lining material in the pan bad news

Sounds like the clutch is going out.

check brakes tires steering , check if engine smokes after sitting for awhile just when u start it , check all lites heater radio power windows check if oil is clean drive it and see if tranny shifts in all gears

It seems like to much of a coincidence that it started after you changed the trans oil. You, or someone may have used the wrong oil. Modern automatics are very sensitive to the exact factory recommended blend. Dump the oil and go to toyota for the recommended lube and start over. Be sure the trans is filled correctly...only up to the hot mark if the trans is hot, not just the engine.