Side Window Problems

[72Thunder]

Hey all...

I am on the homestretch of restoring my 72 C10 and admist the replacement of most door parts we have snagged a problem.
I have an aftermarket door, window regulator, sash channel and all rubbers/seals. Vent window assembly is original along with the window. My problem is that after everything is all good and tight in the door and like it should be, my window rolls up and the front seems to go up all of the way but the back of the glass stays down about 1/16" to 1/4". We have tried adjusting and tweaking every possible component and still no luck. Like I say, all of my stuff is aftermarket so I'm thinking that is my problem. Any suggestions on how to have the back of the glass come up so it can seal?

Thanks in advance.