I think when I installed mine, I saw an adjustment screw on top. If it's like my dodge, you loosen the nut, tighten the screw with a hex key, then tighten the nut. My Hanes manual gave a spec on max adjustment. It didn't help much but mine on my dodge was horribly loose. The inch you're getting both ways is pretty normal. I replaced mine when it was leaking rather than just the seal, in hopes of tightening it up, but new still gives an inch either way.