99 explorer engaging gears problem

[Mr. JEX Limited]

Hello, first of all I have a 99 explorer v8 5.0L 2wd auto transmission 4R70W and I have had a problem with shifting into gears for the past month. When I shift into reverse, I hear this clunk and my truck jerks when it catches and I was told to check and replace my u-joints. I replaced my u-joints and the clunk is still there.

I searched around the forums and found out that I need to re-grease my slip yoke. I had it greased this morning and the clunk is still there. The mechanic I trust noticed I had a transmission leak but he could not tell where the leak was coming from because it was sort of all over the driveshaft.

The mechanic checked the trans fluid level and it was full and he said it may be a bad sensor or a seal that has given up. It's something that is making the gears engage hard and I came here to see what do you all guess it is because I am at my wits end with this clunk and jerk problem and I don't want to keep servicing parts that don't need to be serviced and throwing away money.

Thanks

 

[Mr. JEX Limited]

*UPDATE* I went to my local mechanic and he checked out the leak more and found out that the leak was coming from a missing or bad sensor. He didn't know what sensor so I have to go to a transmission specialty shop. I am going on Glacier's statement saying that it's the TFT sensor.

 

[Mr. JEX Limited]

any advice?