[steelybill]

The manual for mine also mentions intake manifold gasket leaks as something to check. In the old days we checked for manifold vacuum leaks by using a squirt type oil can with some gasoline in it, and dribbled some along the manifold gasket edges. If it was leaking, the RPM picked up.
Did you get a look at the MAP sensor hose ?, and the MAP hose fitting/opening in the throttle body?
My manual also mentions the HEI ground connection. I'm not sure where thats located on your car. There is a black wire on the coil in the distributor, which is the coil ground wire. Maybe that is what's referenced. The distributor schematic shows the grounds to be on/in the distributor housing itself. The black/red wire in the plug for the distributor is the reference ground to the ECM. Check that connector for loose fit on the pins etc. Mine was problem.
On mine, the ECM , the climate control, and blower motor ground is on the Alternator mounting bracket. You could check if yours is there, and it's condition/torque on the fastener.
Also, there is a junction block on the R/H shroud behind the panel (dash), sort of ahead of the door post area, with 26 connectors plugged into it.
Another one is located behind the panel, to the right of the steering column.

Some of my problems were fixed by simply un-plugging and re-connecting stuff, which likely helped make better contact in the connector pins etc.
That's how I made the cruise control problem go away.

The manual ground schematic shows splices in the ground wires (scary) They are usually in the wire bundles though, and well protected.

Hope all this helps a bit.......
BILL

Oh yeah, the ground at the jump-start junction block near the battery is also the ground for the fuel data center, and climate control panel (control head) That's worth a look too.