i connected an amp clamp to the battery and messured current draw while cranking with a the 2 channel entry level pico scope. saw the dip on the screen.

 

So was the scope was on the battery or on the ignition circuit for each cylinder?

 

Oh, were you were doing a relative compression test? Is that what you mean by seeing amps dropping on cylinder 3 when cranking?
https://autoditex.com/page/relative-...test-67-1.html
I see why you might think it was mechanical then.

 

Yes, relative compression test, I put the clamp on the battery,

 

I did the check over a year ago, I've been driving the truck since then with an occasional "reduced engine performance' (I've learned to bypass that by putting the engine in "Neutral Drive" at red lights or stop and go traffic), looking to get around to finally fix it some time soon...Thank you all.