Iam using EZ Drummer with realband. I think power tracks is similar enough to try and help you.

1.In midi setup there is a checkbox to re-route midi playback to default synth. This may need to be checked or unchecked depending on whether you are using a single synth or have assigned a specific synth to one or more tracks.

2.Ez Drummer is set up so that it will respond correctly to a GM file. Are you referring to the same midi file not always playing all the drum notes, or different midi files? If you are using files taken off the web you may find that the drum mapping does not match. Piano roll will allow you to re-assign the notes to the correct keys.

3.Dragging and dropping the grooves onto a realband track behaves the same way. Here is the work around:
Alternate between two tracks... Drag a groove to the first track, Drag the next groove to the second track and then copy paste to the first track. The grooves must be dragged to an empty track or it will erase the previous data. I believe this a problem specific to realband.

If you are having trouble with vst's,some more info on your setup will enable more people to give you some help.

Bobby..