sometimes.

 

Did you ever solve the problem, it sounds like the same problem I am having in my '05 Sierra.

 

White smoke normally mans it's running rich in fuel.

 

Its eating up all ur fuel dude; white smoke is an indication that even the oil is getting consumed pretty much quickly...

 

YOu said it was a 1990 model? I would say it has worn out valve guides/ seals. My dad's truck did that same smoking thing. We replaced the guide seals and solved the problem, but that was over 200,000 miles ago and it is really using oil now. What do you expect from a well used Chevy Silverado with teh original motor in it that has been used form street racing to hauling everything every where around the state and city and the deerlease of course, but it is still trucking... just not as fast and fuel efficient as it was. However it is a 5.7 liter.... not a 4.3.