Rear Window Gasket Help Please

[KTLX]

All, I went to put a sliding window in my cab, large window, no trim, followed the direction, used plenty of dawn dish soap and could not get the window to go in. I wound up tearing the gasket to shreds on the inside. Any suggestions. Process I used, put the gasket on the sliding window. Put a small cord in the inside track, held the window up and pulled the cord from the inside. Zip, Zilch, Nada, a royal pain and very frustrating. Before I call the glass shop, is there a better way.