1996 corolla shaking and changing gear problems

[rjousuf]

I have a 1996 Toyota Corrola DX with 130,000 miles and its automatic. For a long time now maybe around year sometimes whether its morning day or night driving around, it has problem chaning gears from 3rd to 4th. When it is around 35 to 40 it changes gear and then from then to around 50, 60, 70 mph, it tries very hard to change the gear but makes the sound that it is about to do it but Not. So after few min it finally changes and the car quites down. Then the whole time driving it has no problem changing gears. This problems happens every now and then and not always....... Then this 2nd problem started few days ago...Everytime no matter how fast or slow the car is going, If i remove my foot from the gas and put it back down, the car makes a cluck sound. It does it each and every time i lift my foot from the gas little and put it back down again. Its also jerk very little when it happens. Someone told me that the car may be low on transmission oil and i should fill the oil. Should i just put the oil in the Dipstick hole or do i have to remove the old one first. I dont think i ever changed the transmission oil. Engine oil is changed howerver every 3 to 5000 miles. Thanks alot for anyones help