@ThereIsNoTry did your car pull fine past 5,000 rpm before the new clutch install? I've read that in some cases a crank relearn can be required after clutch installation. This may be the cause of your issues above 5,000 rpm. If you have the tuner with your car you can do it with that. If you don't have the tuner maybe someone more knowledgeable than me can walk you through the steps to get it done. Below is the procedure for the crank relearn on the SCTX4 I found on the internet.
Crank Relearn
The Crank Relearn or Crank Position Relearn is not something that needs to be done too often and is more common for Manual Transmission Vehicles. On the 2011+ Mustangs you will need to use this function if you have replaced the clutch on a manual or for automatics if the trans has been removed for service. We have also seen occurrences on the 2015+ Mustangs where this is needed after loading a tune file. Lets go over the steps for doing this.
1. Go into the Vehicle Functions option.
2. Then select Special Functions and you will be prompted to turn the key on and continue.
3. From here select the option for Crank Relearn.
4. You will get a Notice about doing this procedure after certain engine repairs, select Continue.
5. Then follow the steps, Step 1 - Make sure no DTC's are present, if non continue. If there are DTC's you would need to clear them first (
Clear DTC's).
6. Return rev limiters to stock. This is not always the case and you can Continue.
7. Start and Idle Engine. Keep the car in neutral and let the engine get to operating temp.
8. Follow onscreen prompts and raise rpm to range listed on screen. Device will show when crank relearn is complete.