The law changed a couple of years ago to allow a regular evading (on foot) to be charged as a state jail felony if the person has a prior evading arrest conviction of any type. Basically, it's just that way because that's the most recent thing the state legislature has said on the subject.
This is known as an ehancement. As Ms. Foley said, the state legislature felt that evading after you had previously been convicted of any type of evading should be punished more severely. You need to hire a lawyer for your fiance because often the state will drop the enhancement or they will agree to a 1244 motion which would allow the offense to be served as a misdemeanor (so you get county good time) or even be adjudicated as a misdemeanor. If this is was your fiance's first felony, Tarrant county also has several programs for first time offenders that laesseb the severity of the punishment. A good criminal lawyer will know what they are and how to get your fiancé shuttled into one of those programs. Good luck.
It is a felony when the person is in a car or when they've been convicted of evading before. It is a State Jail Felony, which has a punishment range of 180 days to 2 years in jail and a fine up to $10,000. There is a good likelihood of probation but he needs to hire an attorney to focus on a reduction of the charge to avoid a felony conviction.
Good luck and hire an attorney in short order.