I have a 1970 chevy vette, 350ci 300hp pretty much stock. The engine has run great for years. However, recently I have been experiencing terrible bogging/missing across the mid rpm range.

Engine starts easy and idles fine. Also runs fine through the entire rpm range when it is warming up. However, once it reaches normal operating temp (still ok at idle and at low rpm's) it begins to bog/miss/buck in the middle rpm range. If I work it above ~3,500 rpm, it grabs hold again with smooth good power.

I am not an experience mechanic. Pretty much learning as I go. Any ideas or simple things to check? Any help is much appreciated.