[Putershark]

I would start looking at...

• Possible loose ground wires at the engine block (does not take much a voltage drop to confuse any ECU) would just take any grounding wires and clean under them and re-secure all on the engine block. Matter of fact, you drop below 10.5 volts and many ECU's drop into a limp home mode with no timing advance curves and these engines start to run very poor.
• Clean and re-secure all battery connections.
• If you have a A/B battery switch, make sure all connections to the back of the switch are secure and use locking washers to help prevent them from getting loose again.
• Engine charging system output at the higher RPM's.
• Spark plug wires breaking down under stress or arching past the plug boots to the block. 10 ohms or higher resistance on any plug wire is asking for problems.
• Fuel injector leads clean and secure.
• Ignition switch wires all nice and tight and no vague spots (hard to explain) when moving the key from the start to the run positions.
• "Very Carefully and in very small amounts" spray some throttle body cleaner while the engine is running and warm and see if you can find a vacuum leak in a manifold or vacuum line. The engine will increase either increase in speed or stumble pending on the size and type of the leak. What you are looking for is a "change" in engine RPM (up or down) from it's normal idle speed.

I am sure others will cook up some other places to look to go