Well well next problem has risen, actually something it's had for a while but I assumed was worn suspension parts that have now all been replaced.......
The symptom is as follows: Driving over 45mph on a straight and smooth road 5th gear and let's say cruising throttle maybe 20% all is well. As soon as I lift off the throttle leaving the truck in gear it seems to push over to the left. If after I left out I then apply the throttle the truck will push to the right. Both are dramatic enough to need steering input to correct.
At first, I assumed it was the busted ball joints/steering arms however, since replacing them all I think it may have gotten worse. There is literally no steering arm, spring, shock, joint, or bushing that hasn't been replaced in the last 365 days except for motor mounts which don't appear to have any abnormal flex.
Totally spitballing but maybe the G80 doesn't like the sudden application or revocation of power and it's pushing the truck one way or the other?