transmission slipping

What is your question?

I was driving down the road when I thought the engine misfired. I drove home, I had to climb a steep hill, again it acted like misfire again. Check engine light showed both o2 sensors reading lean. So I checked fuel pressure which was in spec. I replaced both o2 sensors with no change. Only at operating tempature will this problem arise. I took the Blazer to a mechanic, he told me transmission was slipping and these electronic transmissions will not allow the engine to rev past 3500 rpms to prevent overrevving the engine. Is this true or do my problems lie somewhere else?