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Coolant temp sensor, most likely. It's probably telling the computer the engine is much hotter than it is and going too lean to run properly.
That or your fuel tank isn't venting. Try running it with the gas cap off to rule that out.

 

Cat converter is a possible problem as well, since it is limited on revs. When it loses power, can you back off the throttle, and it feels like it picks up speed a little? Can you feather the pedal to get it to speed up? (back in and out of the pedal to get it going)

 

Since it runs ok for 10 miles or so, its a long shot. How about the fuel pump, does it make a lot of noise as it heats up like many GM pumps do?

 

My money is on either Ignition module or cat converter. It might be worth unplugging the intake air temp sensor to rule it out.

 

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Even a newer cat can have issues, I'm leaning more toward a cat problem, It will probably put your CEL on when trying this but when it starts to do this again leave the engine on and loosen your fuel cap, if it resolves the issue than it is vapor-locking (just a simple test) Let us know how it goes

 

sounds like an exhaust restriction too me. Doesn't matter that you just put a cat on a while back. I have a pressure gauge that you screw into the O2 sensor bung to measure back pressure but a real redneck way of diagnosing this is to just remove the cat and drive it down the road. If this is the case you need to figure out what caused it to plug before you lay down the bucks for another one.

 

Probably should ask which motor we are dealing with here, 3100 or 3.4 DOHC?

 

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Once plugging, temp is not as much of a factor, as it is an exhaust restriction at all times. The computer can try to adjust to deal with it, but can't totally compensate. Does it lack for power, then if you back off the throttle a bit, it seems to pick up? A lot of times they start out good, then choke up.

 

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Thats weird on a 96 it should have set a check engine light. My 93 plymouth had a O2 go bad, it would idle fine and then when I took off from a light it would sputter, puke black smoke, then go into open loop and run fine until I came to a stop again. I got 17mpg on the hwy when I would normally get 28

 

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