There is a procedure in the book but basically you pop the clip away so the cable can move, then WOT the pedal and pop the retainer clip back into place

 

is this at the intake or at the transmission. Ive also notice the pop on white head of the cable at the throttle body is broke, though it seems to stay on. could this be an issue?

 

I think that is the cable and that could be your problem.

 

saw a youtube video where the guy had the same jssue on a 4.9L. to test it i pulled the vacuum hose off the EGR and plugged it. its not perfect but it does seem to run better.
Could bad injectors cause the shaking too? the fuel pressure was ok up to them , but they are the original.30+ year old injectors

 

When you disconnected the vacuum line from the EGR, was it sucking air before you plugged it? There should not be any vacuum going to the EGR at idle.
Dirty injectors can cause a missfire, but the age of them is irrelevant. I've never seen an injector actually go "bad" on one of these trucks without being physically damaged. But I have seen plenty get dirty, even dirty enough to get stuck shut.

 

No it wasnt sucking air at idle. It was working as it should. ive also had the EGR off in the recent past and it works fine as is

 

Turns out the rear ujoint of the driveshaft was froze ip. one way the was absolutely zero.movement. Replaced and its a ton better. Still has some shake when in overdrive , especialy under a load like uphill, but its better. seems like a miss

 

runs good now but still shaking in overdrive

 

I would replace all the u-joints

 

i replaced both ujoints