Ko I have an idea what's up but I'd like to have some other opinions thrown at me if you don't mind. The Blazer, with a 350, is pinging (clattering lifters) really bad at highway speeds of 60 and above i.e. higher revs after a trip of say ten miles or more i.e. really warm. At the beginning of a drive no issues at all. Makes some obnoxious noises at rather high street rpms as well but it's a different noise. I keep retarding the timing but it doesn't seem to be making any difference. If you need some more detail then that's cool. Fire them questions and I'll answer as best as I can. Any and all thoughts appreciated. Thanks in advance.