1997 Chevy Monte Carlo Loses power

I have a 1997 Monte Carlo and for the past year when you are driving whether in town or on the highway, it just loses power and when you give it gas it won't accelerate. It does not die and you can put it in nuetral and rev the engine and then it suddenly goes back to normal. I started doing it about every three months but lately it has been about every week. I have taken it to my mechanic three times and he has hooked it up to he computers but nothing shows up and when it loses power there are no lights that come on. I don't know what to do or how to get it fixed. My mechanic thinks it might be the sensors but is not sure which ones because of nothing showing. Any help would be very grateful.