squeal sound while shifting on heavy accelration

hi :
i'm new to grand marquis ...
i bought 98 grand marquis 133,000 mile dual exhaust .
k on heavy acceleration and while the car shifting to the next gear i hear squeal sound ...+ my car jump like some one hit me from behind ...

it doesn't do that in normal driving + i found when it's not worm(after few minutes of driving ) the sound doesn't come out + maybe the jump is less powerful ...

trans fluid changed 4 months ago + it's good no bad smell etc..
some one told me the squeal from the belt !!? no idea about the jump.

in this video you can hear the sound(second 6) .. it's not my car or any thing it's just the same sound i hear when mine shifts ..

https://www.youtube.com/watch?v=4K3bsvmk0IAe

pls help i really don't know where to start ... TY

Hi Emperor,
The kick in the pants is from a hard shift usually this type of shift is a little delayed this can cause the motor to rev higher than normal causing the belt to squeal especially if the belt is old. I had that same squeal from my belt when mine would shift hard.

When you serviced your Transmission did you go with standard Trans fluid or the recommended Synthetic Fluid? Also was the Transmission flushed or just the fluid changed?

A new belt may be in order as well check your serpentine belt for cracks or other wear issues.

Thank you sir for replaying :
i thought the same .. but you know this is my first car so i don't know much ...

yes the trans delay so the rev get higher than it should ...

but this is a sub problem ... right ?

the main problem is the trans delay .. ?

i forgot to write about another problem in the trans!! .. when i shift it into D it delay about 2-3 sec then it engage .. the fluid level is good ...+ the car sound goes down like it will stall when it shifts + the head lights and dashboard lights are weakening.. i think it has nothing to do with the main problem ..

so you asked about the fluid .. well i bought the car and the owner told me he changed the fluid
but as much as i know ..
1-it's just changed not flashed .
2- i asked him about the oil type he said he he doesn't know !!!!?>?>?> but i think the mechanic just used type M .
i was thinking about changing the fluid .. do you think this will fix the delay ?
and what type should i use ? the manual says type V .. should i use this or the newest one ?

last thing , is the kick or the delay harmful for my trans or motor ?or does it mean i'll need a new trans soon ?
thanks again

Yes the main issue is most likely the trans delay

On the fluid you have the Mercon V where the V is the roman numeral 5 so "Mercon 5" but you have two types of Mercon 5 fluid, standard transmission fluid or synthetic transmission fluid. Ford released a service bulletin recommending that all Ford AOD Transmissions should use synthetic fluid due to potential issues with the Torque Converter.

You may want to changed the fluid, I would recommend doing this at a reputable shop and paying for the synthetic fluid or buy and bring your own. Also in high millage transmissions I like to add Lucas Oil's Transfix as well. If the shifting issues continue you may need just the transmission solenoids replaced or potentially a transmission rebuild only a good transmission shop would be able to tell you for sure.

thank you sir you really helped me , i'll follow your advice .
thank you.