97 grand prix gtp wont start

I have a 97 gtp that instantly died on the highway going 70
mph. The steering went tight along with the breaks being
harder to press down. It had a half a tank of gas. Car has
175k miles. Ive checked for fuel which its getting. The fuel
pressure was 60 psi on first crank then lowered down to 55
psi. A mechanic had told me it was probably a fuel pressure
regulator before I tested the pressure an since there not to
expensive I bought one an put it on. Well the car still wont
start so I tested my plugs and coils for spark which they all
have. Before the car died there was a code thrown for a faulty
o2 sensor but ive heard that an o2 sensor wont cause a no
start issue. Im leaning towards possibly a bad injector or bad
throttle positioning sensor? I had to replace the tps about 6
months ago an when I installed it something went wrong an
it was catching inside at the wrong moment so it was taking
an extra long time for my car to shift so I took it off an put it
back on correctly an has been working since but im
wondering if I ruined the spring an the tps failed early. I just
dont understand how it was running fine on the interstate for
an hour an a half an it just died? Any ideas would be very
greatly appreciated. Thank you