Vortec 4.8 / 5.3 differences: GM used a shorter stroke crankshaft in the 4.8L and a longer connecting rod. 99 to 03 or so, the 4.8L's all had completely flat top pistons. 5.3L's had a slight dish. However, after about 2004 sometime, the 5.3L's could have true flattop's.