Loss of power after driving for about thirty to forty minutes

Hi,

It sounds like there could be an issue with fuel pressure or even a plugged fuel filter.

When this happens, is there anything that seems different? For example, do you notice the exhaust having a different odor, or see smoke from the exhaust? Is there any rattling in the exhaust? Is there anything that seems to prompt it to happen? For example, climbing a long hill.

If the fuel filter has never been changed, it would be a good idea to do it. It may or may not be the issue, but it is basic maintenance. If you look at the pics below, it shows the location. Pics 2-4 are the directions for removal and replacement.

Next, it would be a good idea to see if there are diagnostic trouble codes stored that may indicate where the issues are coming from. This truck has an OBD1 system and doesn't require a scan tool to retrieve codes. Follow the directions in this link and let me know if you find codes and what they are.

https://www.2carpros.com/articles/mitsubishi-trouble-code-definitions-and-retrieval-procedure-for-odb1-system

You will need a voltmeter or multimeter for the test. It's really easy to do.

Let me know what you find. If this doesn't help, we'll continue checking.

Take care,

Joe

See pics below.