I have a 2003 Mazda Tribute V-6 4x4 with 28k miles. Recently I have
noticed that when I am driving at speeds between 45-60 mph and
accelerate, it jerks before it starts going. It doesn't happen at
other speeds. It also accelerates smoothly through that range if I am
starting at a lower speed.

Does anybody have an idea of what might be causing this?

Thanks,
Jeff