Rear Blazer window won't fully go up

[Ski-me]

89' K5.

I replaced the tailgate with a new(er) one that had no rust in it. Replaced the lower channel that supports the window (glued in with silicone). Put everything back together and works like a charm!

However, the window doesn't go all the way up into the felt channel in fiberglass top. It touches it but doesn't fully go within the channel.

The felt is the original one and I'm wondering if it is somehow squeezing the glass to tightly to prevent it going all the way up?!?

It looks closed from the outside, visually. But if I go through a car wash, water comes in pretty good at the top of the glass.

I'm wondering if I shave off a little of the felt on the inside, it would allow the window to go the rest of the way up....looking for ideas.

Thanks!