Problems like this are frequently caused by a lack of boost pressure reaching the ALDA. The ALDA is a mechanical device atop the injection pump which reads the boost pressure and adjusts the fuel delivery accordingly. More boost, more fuel. If the ALDA never sees boost, it never increases fuel, and the result is ~80HP.

I don't have a picture of the ALDA handy. It's on top of the injection pump. Has a blocked off opening for a screwdriver adjustment. Also has a vacuum (well, boost really) line running out the side. This boost line goes to a switchover valve on the firewall. From there it runs to the rear passenger side of the intake manifold. At the intake manifold it connects via a hollow bolt. This hollow bolt is known to clog with EGR stuff and/or oil crud (technical terms there). When it clogs, no boost.

To troubleshoot, remove the hollow bolt and clean with solvent. Remove the tubing and inspect for cracks/breaks. Be sure to check the rubber connecting pieces as well - these sometimes develop cracks. The threeway valves on the firewall are occasionally known to go bad, so you can bypass it to test. Don't run without the threeway for any length of time - this is your overboost protection.

Most likely this 15 minute job will clear up your problem.

- Jim