Nothing in your post suggests that you or your wife have any basis for suing the officers or the police department. Nothing they did violated any of your rights, and you suffered no legally recognized harm. You may complain to the police chief if you wish. But bear in mind that the two of you contributed to the unpleasant encounter, too.
Texas has NO law about driving on methadone any help or suggestions that we should do to address this issue would be greatly appreciated.
The Texas DUI statute prohibits driving under the influence of ANY substance, whether legal or illegal. Texas Penal Code (PC) section 49.04 is the basic DUI statute, which states:
Sec. 49.04. DRIVING WHILE INTOXICATED. (a) A person commits an offense if the person is intoxicated while operating a motor vehicle in a public place.
(b) Except as provided by Subsections (c) and (d) and Section 49.09, an offense under this section is a Class B misdemeanor, with a minimum term of confinement of 72 hours.
(c) If it is shown on the trial of an offense under this section that at the time of the offense the person operating the motor vehicle had an open container of alcohol in the person's immediate possession, the offense is a Class B misdemeanor, with a minimum term of confinement of six days.
(d) If it is shown on the trial of an offense under this section that an analysis of a specimen of the person's blood, breath, or urine showed an alcohol concentration level of 0.15 or more at the time the analysis was performed, the offense is a Class A misdemeanor.
PC § 49.01(2) defines the term "intoxicated" to mean:
"(A) not having the normal use of mental or physical faculties by reason of the introduction of alcohol, a controlled substance, a drug, a dangerous drug, a combination of two or more of those substances, or any other substance into the body; or
(B) having an alcohol concentration of 0.08 or more."
Note that this definition covers a lot more than just alcohol and illegal drugs. It's not limited even to controlled substances (which includes a lot of legal drugs like methadone). It covers ANY substance that impairs your ability to drive. Bottom line for you is that you commit a DUI offense if you drive while impaired by methadone.
Note that if the DUI occurs with a child under age 15 in the car, PC § 49.045 raises the severity of the offense to a state jail felony.
You may read the entire Texas law on this here: Texas intoxication laws