Smoke???

[jsbihn]

Ok so i am driving home this week and after about 1 hour or so on the road I exit off the interstate. I slow down and then stop, and I see from the rear view a whitish smoke. the smoke then moves to the front (remember I was stopping), and I could smell there was a bit of an odor to it.

The truck only does this when travelling for a bit of time at high speeds, around town it doesnt do it

Ok, so the car runs fine
I havent seen any issue with it.
I started to think, maybe it is the cats because those things are shot and are sounding like tin cans rattling around rocks.
But then I also wondered if the valve seals are leaking.

of course all of this may be wrong and it may be something else completely

I am wondering what you think it is
Also, if it is the valve seal, is there like a good additive that will refresh them until I can get the time or the money to get these done.
and if it is the cats, then thats cool because i was thinking of cutting them out and having a pipe welded in.

the truck has 107k on it

i appreciate your ideas