Caravan only gets to 25mph then slows

My friend give me this account:
The car would only get up to 25 mph and then it would go slower and slower until she would turn it off, then restart it and go through the same cycle til she got home and parked it.

And now she can get it started but it won't idle. I am attributing the idle problem to the cars computer, that probably need to be rebooted but now the battery has drained. I only mention this in case there might be some connection to the problem mentioned above.

In that the car will move, albeit only 25 mph for a while, indicates that the differential is okay. Is there something in the computer controls and/or sensors that can be checked short of a complete rebuild?

It is a 3.3 flex-fuel engine. The year of manufacture is 1998.

Is the alternator charging?

What kind of fuel pressure do you have?

I can't answer that just now. Shall I assume from your questions that no output from alternator would allow computer to not get sufficient voltage to manage the engine including the fuel pump?

My questions where to get you going in a direction. Without knowing what your missing there is no way to give advice on what to do.

OEM computers do not boot, the program is stored on a PROM, EPROM or EEPROM. IF it runs at all it is not a program issue. In any event for the time being you should start out simply by checking things that you would check on the car if it was an old carbureted 1977 smog car. That’s correct check for things like Voltage, Gas, and fire. Then move on to a more educated questions like is Ok cold, Hot, etc?