1988 Chevy S-10 Smoking Problem

I have an 88' Chevy S10 pickup with a 4.3L engine and 4WD. about 6 months ago the engine was replaced because the original was ran without oil. This new engine is the same 4.3L but when it was put in i saw that it was putting white smoke out of the exhaust. Since then the problem has steadily gotten worse. Now that its summer the problem is unbearable. its like driving a diesel with all the smoke its putting out. When it starts getting above 90 degrees outside the truck tends to stall and shudders. [img:1a7fa41a7a]http://www.2carpros.com/forum/automotive_pictures/544601_88Chevrolet_S10_1.jpg[/img:1a7fa41a7a]