Terry, the 250-CR's had a similar problem. Rather than trying to replace the headliner (BIG job) or trying to squirt more glue between the headliner and the deck (doesn't work for more than about a week), go to your favorite large, orange, box, retail giant that sells home improvement stuff.
Buy a handful of stainless steel, phillips- or square drive-head screws (about 3/4-inch long) and an equal number of "screw caps" (a plastic cup-shaped "washer" that also has a cap that snaps onto it and covers the screw head) in a complimentary color to your headliner. Next, make yourself a square template of a dimension that suits your eye out of thick poster board (maybe, about a foot square) and drill a 3/16" hole in each of the corners. Stretch a string from the center top of the forward bulkhead to the center top point of the rearmost bulkhead in the cabin (along the centerline of the boat, but along the headliner). Place the template next to the string and mark the four holes. Move the template longitudinally and also laterally so that two of the drilled holes end up on two of the previously marked holes, then mark two more holes.
Eventually, you'll have a pattern marked out over all the area that's sagging. Using the screws you bought, drive each one through the headliner and into the decking above. Put the cap on the screw and move to the next. Eventually, you will have an eye-pleasing grid of covered screws that will hold up the headliner.
Some might suggest spraying 3-M Spray Adhesive behind the headliner (that's what Crownline originally used, I think), but I'm here to tell you, it doesn't stay.
DILLIGAF
(Does It Look Like I Give A _ _ _ _)
1996 250-CR