I understand that the slides are specifically rigged to go in slightly further at the top, to ensure the top seals are tight, to keep rain out, but 1.5" seems excessive.
On our GT325, I would estimate the slide-out walls are maybe 1/4" out at the bottom when the drive starts to slip. The bulb seals are compressed, but not completely flat. When the slides start to go out, the top moves first, then the whole thing ends up with the outside wall vertical and all the inside bulb seals equally compressed.
Frank and Eileen
No longer RVers or FR owners