302 motor/ getting blow by out of the oil fill vent hose/smoking really bad at high speeds out of hose/ changed out pvc valve already/ not sure what to do next?? can anyone help me??? Motor is still very strong miles on truck is 137,000

 

You didn't provide any mileage info which could help answer your question, however, so you know where you stand it would be a good idea to run a compression test. Based on those results your next steps might be to pursue the remaining possibilities. In either case it appears compression is getting into the crankcase and it could be from one or more cylinders with worn/ stuck piston rings. Let us know what the readings were for each of the 8 cyls.