If your van still smokes on startup after 9000 miles its not going to quit. You most likely have a valve guide and or valve seal problem. It very will might be that someone knurled the valve guides rather than put new guides in when you had the heads done You dont need to wait any longer to put synthetic oil in it. I'd do it whenever your next oil change is due. there are some very good transmission additives out their that might help. My 92 GMC transmission was very suspect at 120,000 miles I thought it would go anytime. I flushed it good ,changed the fluid and filter and put a good, (not cheap)additive in it. It now has 168,000 miles and still going strong. And, I have been tough on it pulling horse trailer ,car trailer and equipment trailers. I'll keep my fingers crossed. Back to the smoking on startup. I am assuming that the smoke you are seeing is oil smoke. If so I stand by my prediction.