Runs Rough Under Load

[Schurkey]

I have no idea how a "driveline" problem can cause symptoms you've described as "misfire".

You never described the fuel pressure under load.

Have you ever tested spark output using a spark tester calibrated for HEI?

Your ECM seems reluctant to store codes. Seems fishy. I'd try to deliberately set a code or two, and see if the computer is capable of storing it. No stored code = failed ECM.

And as always, get a scan tool connected, and look at the data stream WHEN THE VEHICLE IS ACTING UP.

 

[GoToGuy]

The driveline isnt the cause, the engines lack of power/ performance affects driveline.

 

[97Yukon4dr]

Just wanted to post this just incase someone looks at this thread later on.... I removed my throttle body today for normal cleaning, and when i peeked inside the upper intake manifold I saw a clean moist spot. aka my spiders are leaking. I will be replacing them soon and converting to mpfi.