transmission slip when accelerating
 

Hi,

i have Ford Freestar 2005 V.6 with automatic transmission AX4N. i am his second owner wince 5 years.
Actually since few months, it slip (each time) i accelerate as soon as i reach 10km to 20km. got a boom/ kind of suddnely push-up.
what i have did until now,
there was recall letter from ford to change torque converter and they change it.
fluid is flushed and the level is ok also.
The thing i dont i understand why it happen only when the speed reach between 10-20km but before or after nothing happen, all is well. what it could be?
Also, when while reversing with warmed transmission the gear seem not be engaged there is alway a delay of 3 to 5 seconds. but with cold transmission it engaged on the spot.
Can some help me to find out the problem please .
Please ask my any questions info need more. thanks
Hope i was able to explain my correctly.

Slipping Tranny
 

Mine does the same thing, only when it is in cruise control. Check the transmission speed sensor (located on tranny housing) and check/replace each wheel sensor. :o

how it can do in cruise control? the cc start from 48kms..
i think there is a issue with fluid pump drive shaft which is connected in torque convert,
i saw one video on youtube and the guys was talking about that,
dont know exactly where is the problem

Check to see if the torque converter was ever replaced in recall. You can give VIN to your local Ford Dealer and they can look up any recalls that have not been done yet. I just found out that mine was slipping and it did not have the torque converter replaced by recall.

As i mentionned in my question they have changed it i have the receipt that they gave me. the job was done in ford dealer shop by ford mechanic, not the private or general mechanic.

actually i dont know, what parts become active (between 0 to 20kmph) when we press accelerator. you know what i mean.

anyone interested to help me to solve this problem?
actually it happen only when I start moving from a stop. it's very jerky, and a I have to feather the gas to get it to smoothly engage.

That sounds like the TCC solenoid in the trans, it controls the pressure and if weak or sludged could cause low pressure at idle , low throttle which would keep the clutches from engaging. As a habit I change any TCC solenoid if I open the trans for filters etc. even if I have to drop the side of the engine down.