white smoke coming from exhaust when running

Indicative of failed head gasket .. Suggest *combustion leak test*. .. Head gasket failure from coolant passage to combustion chamber will NOT show up in the crankcase oil..! .. A lot of people mistakenly think a blown head gasket will automatically put coolant in the oil .. That's not always the case, especially on a pushrod engine, like the one in your truck! .. However the exhaust 'steam' will surely show the effects!

What he said unless real bad and driven without being fixed.