I saw a 1996 Tahoe at work today with the 350 Vortec and it had 413,000 miles on it! The owner said he had to replace the original transmission but as far as the engine goes it had never been opened for a repair! It looked good and sounded even better with a nice exhaust on it. He said he uses Castrol GTX 5w30 changed every 3,000 miles. Thought that was pretty neat and wanted to share it.