Is the engine speed higher than usual? That will cause a tug.
Have you adjusted the throttle valve (TV) cable if your car has one?
Also, check the transmission diagrams for a "forward abuse valve" to see if your transmission has one. Transmissions often have abuse valves for forward and reverse which bypass the normal apply orifice to cause a quicker apply when the driver shifts into gear while stepping on the gas. This is done to prevent clutch burn up. If the valve gets stuck open all the time, then you will get harsh engagement even during normal operation.
"The unexamined life is not worth living." - Socrates