T660 front end wandering across road.

Check your rear alignment, worn bushings will let the drives push you around.

 

This may sound stupid, but here goes anyway. In 99 I bought an int 9400 in Joplin Mo and drove it back to New Mexico, at first I thought it was just the roads as it would sometimes wonder, but it did it on familar roads, so I went over it and could find nothing wrong. I took it to alignment shops several times over the next two months, but none of them corrected it.
Finally on a bad stretch of I 70 in Utah the cab bottomed out a couple of times and that hurt. I was going right through the house anyway, so had my wife pick up some cab shocks, it cured the wandering, I guess the cab was just jostling me enough that I was the one doing the wandering, a few months later I removed the cab faring, and whoa, it now drove like a real truck.

 

Wander, not wonder. Aaarrrrgh!

 

the front end is "wondering" what the hell your doing up there... Keep both hands on the wheel, not just your left one!

 

Sounds like a loose nut behind the wheel to me...

@Sekots is your alignment good, not just the front end but drives also. Make sure your 5th wheel is greased. A trailer on a rusty 5th wheel will "grab" your truck and push it around