Could it be possible that molars have shifted into different heights. i'm not feeling a complete uniform seal all around.pre molars seem to barely tou?

Might be a tongue : You might have a tongue rest posture issue. If your tongue parks between your teeth then over time your teeth will adapt to it's presence. If your tongue is parking between your premolars, then they will not touch when biting down. An adult tongue is supposed to park in the roof of the mouth. I would recommend a consult with a dentist/orthodontist familiar with tongue functional issues.

It is possible: Teeth are always moving, just in very small increments. What keeps them in one place is the forces around them reaching a balance. If this balance gets disrupted, the teeth can move noticeably and your bite can be affected. One common cause of disruption is gum disease, which destroys the bone that anchors the teeth. Another cause is tooth loss. See a dentist and be examined.

Have it evaluated: Have your bite evaluated to see what's going on and why. There are many reasons for teeth to shift. Some people have greater sensitivities and awareness than others. What you feel may or may not be significant.