As people mentioned, Heavy TFU already has a 10% debuff on speed.
Also, in case you missed it, some changes are coming to the update that was realeased the 1st of december in regards to TFU, just be patient
1. People already use cars as impenetrable shields during shootouts and we don't want to encourage that behviour.
2. TFOs would be able to just jump into the SWAT van everytime they bleed in order to heal up
3. Driving while healing is extremely unrealistic