I have a 2000 Gmc Jimmy 4.3L 4wd which up to now has been a great vehicle for me. The problem its having is that the engine misfires under load meaning mostly uphill or passing, The engine does not misfire at idle or if you rev the engine under no load, I have not begun to trouble shoot so i thought id give this forum a try first.

 

It sounds like a lean condition instead of a misfire.