Spooks can be a pain in the ass some times. They get moody in certain water. Some places they just will never fish well but there are a few things you can do to get the to swim a little better.
First thing like cchobot said, tie on with a direct loop. No
snap and definitely not a tight knot. You want the spook free to dart and slide in each direction along the surface. A tight connection will impede all but the largest of spooks from moving freely. Fish it with the rod tip pointed at the plug and give the tip sharp downward jerks to get it walking and sliding. If it digs in, drop slack in the line and wait for it to come up.
Second, not all spooks were created equally. The two you are talking about definitely work well, especially the jumpin minnow. I've rarely had the JM dig in, but if you are, lose the snap and maybe go down one hook size.
The sea pups can be really tempermental. Try going down a hook size in the belly and tail or belly only. Try to get the ass down in the water a little better. Buoyancy has been an issue with these guys IMO as well as eye placement in the nose. Usually an eye offset just a little bit ffrom the centerline of the plug (offset down) helps to keep the plug up. Maybe try turning the eye of the seapup horizontal and bending it down. Maybe I'll try that and let you know.
Try yozuri hydro pencils and some of the big heddon zara's. The huge ones. Both have eyes offsett on the bottom of the nose and stay up a lot better than most of the competition. The yozuri especially is a highly underated spook and can hold it's own next to the JM anyday. Works on bigger fish too. They make the hydro pencil in bone color now too.
Hope this helps. Good luck.