Smoke From My Truck Exhaust?

I drive a 1988 Chevy Blazer 4x4 5.7L TBI and have been experiencing some problems with it. First of all, it has the original engine in it with about 150K+ miles on it. As far as i know, it has never had any major repairs on it and has always ran faithful sense the day I purchased it. It has always smoked a little bit when i start it, but then once it warms up, the smoke goes away. About 3-4 months ago, I noticed that even after its warmed up, it still smokes, not really heavy, but enough to leave a pretty good smoke screen behind my truck. I have thought it is the valve guide seals. Well, i took it out the other day to get a bite to eat, and i floored it, and my engine stopped for a good half second to a full second, then kicked over and took off, I looked in my rear view mirror and saw that it was pouring out smoke. I look in it every day now when i drive and it smokes all the time, and even after i turn the car off, it smokes. The smoke doesn't really look blue, and ive been told blue smoke means its burning oil, but it isnt pure white. What is wrong with it? is there an antifreeze leak? Blown Head Gasket? Valve Guide Seals? I recently changed the Spark plugs, and fuel filter hoping to smooth the ride out but when it gets into its " heavy Smoking" phase, the engine seems like its trying so hard to push while Bellowing out smoke. Help!!! I have Pictures if that would help!