I know that this question has been asked before. But hears mine... I park my 83 K5 in my driveway with the front facing down hill. Its on a slope and when I start it up I let it run for 2-3 min to warm up. Then Apply the breaks, Pull the E Break, and Slowly put it into 3rd. Once I take my foot off the break and start to cost down hill. The first 6 inches POP. Something really SNAPS. But that's the only time that it occurs and its not all of the time. Once in a while it happens. Could it be the TRANY and TORCH conv. slipping ur something... PS. It is the factory Trany. No work done to it but routine oil and filter change.