So a buddy/co-worker of mine moonlights at an Advance Parts that is attached to a warehouse. He arrived this AM with a 1 1/8" MC listed for an 89 D150 (a CarQuest one, no less and not their house brand, fruit of a merger). $27 and he'll take it back for me if it doesn't fix my problem.

Looks like I'm going Air Force Method for this step (throw parts at it until it works).

If this works, YAY! If not, I'll pick up a pressure gauge and continue in a diagnostic fashion.

I'll report back, and thanks for you input thus far everyone.

Chris