Automatic transmission problem

Automatic transmission delayed in changing gears. Stay's too long in gear and high rpm's. I also notice a high fuel consumption. Last two months my car had an idle problem swinging between 1,200 and 2,000 rpm's. This happen while driving the car and also in the garage.

I did the following:

First thing I did was cleaning the ICV but it did not help to solve the problem.
Purchased and installed new MAF Sensor, TP Sensor and EGR (ICV). I also bought a set of two O2 oxygen sensors but unfortunately this car does not use O2 oxygen sensor.
By doing all these changes, there was absolutely no change in the rpm's. Last, two weeks ago I notice a big spill of transmission oil on the floor, and after cleaning this I did a check to see where the spill is coming from. The oil pan gasket and oil seal ware okay and I could not find where the leak was coming from.
Three days after the first leak I got another big spill and this time I notice that it came from the vehicle/transmission speed sensor. The o-ring seal of the vehicle/transmission speed sensor was broken and I bought a new o-ring seal. Due to this I decide to change the transmission oil and transmission filter. I have added the “Lucas Transmission Fix” to the transmission oil after reading some good reviews of this product. After all of these I went for a test drive and the Idle seems to be okay, but the transmission stays to long in a gear before changing. I notice also that with a very soft touch on the gas paddle, sometimes the rpm's can go very high. I am driving the car for one and a half week and it still delayed in changing gears. During driving without giving more gas, the rpm's go high and stay for a long time in the gear before changing gears.
Hope to have informed you accordingly.
Nel.