Engine The Rpm Shake

I hope you could help me figure out whats my problem
I have a 2000 Mustang GT V8 Manual Transmission Bone Stock
I recently bought it from a friend of mine
After a month of using it now everytime i floor it on any gear when it hits 5000 rpm or 4500 it starts to stress like
The rpm goes up slower and the whole car starts to shake as if theres something pulling it back

I changed two of my coils because the mechanic said two of the connectors of the coils were loose
and plugs too but the problems still there

Do you think there are more coils that are loose or this isnt the reason for the problem?
 
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