tcpreplay has evolved quite a bit over the years. In the 1.x days, it merely read packets and sent then back on the wire. In 2.x, tcpreplay was enhanced significantly to add various rewriting functionality but at the cost of complexity, performance and bloat. Now in 3.x, tcpreplay has returned to its roots to be a lean packet sending machine and the editing functions have moved to tcprewrite and a powerful tcpreplay-edit which combines the two.
Lastly, please remember that the packet editing code has some overhead- even when not in use. Hence, for the highest performance I always recommend using tcprewrite + tcpreplay separately.