After replacing my oxygen sensors (who's bright idea was it to put the connectors THERE?), checking fuel pressure and vacuum (both normal) I still have a problem running with a load on the engine (can't really run in overdrive until I get to 70) I've decided to rework my fuel rail. I shall replace the o-rings and clean the injectors. Is Gumout a good thing to soak them in?

Then I'm going to put them to my mouth, and test them with a battery to make sure they open and close.

This is the pushrod engine, the fuel rail work seems really easy from the Haynes manual, I can't see it taking me more than an hour to get the injectors out.

Have you checked the fuel filter?