Transmission slips

I had two error codes on my car listed above SL model.
#1 Cylinder four misfire.
#2 P1750 (Transmission Solenoid problem).

I had a hard time shifting between gears (gears would be rough but would shift). First gear didn’t give me problems but the other gears would have a hard time shifting on hills. And the engine would rumble because of only running on five cylinders.

So I parked my car and replaced all the spark plugs (front and rear). I had to take off the intake manifold and throttle body.

When I put everything back together, the car wouldn’t shift at all. You would have to get it to go in high rpm's to get going. (This was before draining the transmission fluid. )

I then replaced the transmission solenoid pack and the P1750 error code went away. The transmission fluid was drained and replaced. (Not flushed out)

It still had the loss of power in the drive and first gear doesn’t have any power. You only get power when you give it a lot of gas.

Once you have a high enough speed, you can let go of the gas and it’ll fall/shift into second gear and then it drives like normal above first gear. The bumpy/struggling shifting is gone and it shifts wonderfully. When it’s in the air, it shifts fine in first gear. But when you put torque on it, it doesn’t have any power.

Reverse works perfectly as well.

The Throttle Position Sensor works just fine and has a current flowing as the manual says.
I adjusted the throttle cable as well.

What could possibly be the problem? I don’t think it’s anything with the transmission because it started acting up when I removed the intake manifold and throttle body.