Driver and passenger Window channel issues

[mpierce9]

Hello - For some reason I can't figure out, my windows will not stay under enough pressure from the channels to stay inside the channels once rolled down. Both channels have new felt. I've adjusted the rear channel forward some to increase the holding pressure on the window to help hold it in place but that seemed to be a temporary fix. Any time these windows are rolled down they fall out of the window channel are rattle around inside the door. This also results in making it difficult to roll the window up.

The channels are original to the truck. Should I invest in new window channels? Could this be a problem with the regulator?

These are manual windows on a 1975 Chevy blazer. All windows are manual and have new felt, all other parts of the window are original.

Any advice is appreciated.