97 Breeze losing power above 40 mph

My car was running fine and then one day started sputtering on the highway like it was losing power or not getting fuel. As long as I kept in under about 50 mph it ran okay and I was able to make it back to town. AutoZone recommended putting fuel injector cleaner through it and that seemed to work, but 50 miles later it started doing it again, only worse. It got to be a constant issue and eventually started dying whenever put into gear. Changed to fuel filter, coil, valve gasket cover, spark plugs. Brought it into a shop and they replaced the cam sensor and gave it back still messed up. Took it to a different shop who had it three weeks. They said they fixed a lot of loose wiring and cleaned up the fuel injectors and supposedly checked every wire and part in the car. They got it running again for now, but once I get it to about 40 mph it still starts sputtering and jerking again. When it does this you can press all the way down on the gas and get no response and the check engine light flashes. The repair shop told me they have no idea what could be wrong with it and can't think of anything they haven't checked. They said they think I will be fine if I don't leave town with it, but since they don't know what's wrong with it they can't guarantee I'll be able to drive even at low speeds without it progressing again. Any ideas?

So what were the codes?

They didn't give me the actual numbers but said the codes told them to check the crank sensor, coil pack, the cam shaft censor. All were replaced, with no change.

have you replaced the fuel filter and had the fuel pressure tested?

Yes to both

Still needing help with this. It seems to be running fine in town, but starts sputtering when I get it over 45-50 mph.

Still needing help with this. It seems to be running fine in town, but starts sputtering when I get it over 45-50 mph.

You could have a clogged cat. You can smack it with a rubber mallet, if it rattles, internals broke lose. You can test it with a vacuum gauge. Or some cats have a test port in front of the cat. You could pull it and see if it drives better. You can google testing cat.
When it does it can you put it in neutral and rev it up or does it bog down also?
Codes are not the miracle fix. Just a diagnostic tool.