95 Maxima stalling and quitting

I just purchased a 95 Maxima Gxe with 70400 miles on it almost 3 weeks ago...After having it for only 2 days it stalled out on me and quit as I was driving the interstate..The motor seems to rev really high then go done to almost nothing. Took it to a repair shop where they diagnosed a Rear O2 sensor as the possible problem, they replaced it. Car seemed to be working fine but after 2 days it did the same thing, revs really high, then stalls and quits when you pull over..I took it back to repair shop where they have had it for the last week and a half, couldnt locate a problem as the computer was not throwing out any error codes, they said the computer could be bad so that was replaced...Supposedly there was some wires that were frayed and burnt to the computer and those were replaced also...Well today I picked up my car after a week and a half said it was fixed and only after about 10 miles it did it again...Does anyone have any ideas?? Nissan is stumped but have read a few posts here and other sites that people are having the same problems so hopefully someone that has gone thru it already can give me a head's up on the problem...This has gotten to be expensive for me--140.00 for the replacement of the O2 sensor and 200.00 for this past weeks rental car, (I purchased the car used--AS IS at a dealership and they dont seem to care that I have only been able to drive my "new" car a total of 4 days since purchasing it on November 13th, so please anyone help..Thank you..

If the O2 sensor was replaced due to a lean code, either the sensor was bad or you have fuel issues.
I've seen plugged fuel filters trip O2 codes and or weak fuel pumps. Did they do a pressure test?? If so what reading did they get? Did they roadtest it with a fuel pressure gauge hooked up and watch it during the roadtest?? If all this checks out something electrical causing a problem....loose or dirty connection/ground perhaps. They need to spend some quality time on your max and try to duplicate the problem with a tech behind the wheel. Hope they nail it for you and goodluck.
Mark