Need Help!!!! Misfire Problem!!!

I Have A 1995 Mx6 With A 2.5 L Eng. I Changed The Engine And Cannot Find My Misfire Problem. The Car Starts Fine And Idles Fine, And When You Open The Throttle Slowley, The Rpms Go Up With No Mis/problem. When The Car Is Idling And You Open The Throttle Quickly, There Is A Bad Mis That Does Not Go Away Until You Release The Throttle. You Release The Throttle, Then It Goes Back To Idling Fine. The Problem Was There When I Purchased The Car And Then I Changed The Engine, And Its Still There. Any Info Would Be A Huge Help. Thank You
/BESIDES ALL THIS I ALSO TRIED A DIFFERENT ECM, STILL NO GOOD

Check your distributor and spark plug leads! That's what I would do?

Also check your fuel filter and fuel pump, it sounds like it's being starved for fuel. If you changed the entire engine and fuel injection and ignition then it must be something you didn't change like the fuel filter pump or fuel lines.

check the fuel pressure before u change the filter. find out the specs and if it low than it could be the filter, feed line, pump, or pressure regulator.