As for checking the timing I’ll be a bit more specific, if the balance belt is out of time it will cause an engine vibration in the RPM range you mention. It could also be the EGR passages as what I’ve found is the ports furthest from the valve #1 & #2 tend to clog up first causing some cylinders to get EGR and the plugged ones won’t, this will offset the mix and cause a ‘miss’ under load. It’s also a good idea to check the ignition system as I find many times that a miss under load is the result of an ignition problem, here’s a video I did on finding voltage leaks that may cause such a miss.