I have 3406B 4MG in my '89 T600.
It's kind of gradually lost power in the last couple months.
Gauges all show normal temps. Fuel pressure gauge above 30 psi, filter restriction gauges normal. Oil pressure is normal. Fuel and air filters are new.
It won't boost til hitting 1700-1800rpms. Until then it's only about 7.5psi. Throttle pedal movement does nothing.
Before this change I used to upshift at 1700 rpms fully loaded and it would keep going. Now I upshift and it takes forever to get up to speed with only 7.5psi til I hit 1800 again.
Going down the road it's not too bad til I hit an uphill and it just drops off, won't pull even mediocre MN hills.
It feels almost like an old car with a bad accelerator pump.
Pic for attention but it has CAT filters and new ATA boots on it now.