For lack of a better term, I'm simply asking if there is any likelihood of a group moving up/or down after prelims, of if they placed 2nd in quarterfinals they are pretty much locked for 2nd in finals?

What kind of gap is there?

It really depends. If someone is trailing first by two points and leading the third place by two points, they're locked in at second. Make it two tenths on either side and nothing is guaranteed for any of the three.

My drum corps is 1.89 behind 6th and 1.115 ahead of 8th.
My marching band is 1.215 behind 3rd and 4.185 ahead of 5th.
My colorguard is 0.155 behind 29th and 0.115 ahead of 31st.
My drumline is 0.28 behind 5th and 1.44 ahead of 7th.

So, it looks as if the drum corps is stuck, the marching band is stuck, the colorguard could go either way, and the drumline could go up.

Thank you for the reply.

Not a problem! Those numbers that I used a rough estimates too, but I would say I agree with your assessment about your groups.

The colorguard actually moved up two placements--I'm happy with a 28th place finish, especially considering they were only around for a week and a half at most.. Everybody else stayed the same.

Updated numbers:
The DC was 1.58 behind 6th and 1.51 ahead of 8th.
The MB was 1.115 behind 3rd and 4.4 ahead of 5th.
The DL was 0.135 behind 5th and 1.66 ahead of 7th.

The CG finished 0.42 behind 27th and 0.33 ahead of 29th.

So, it's looking like drum corps will be locked, though I did cut the lead down a little.
Marching band will also be locked, though again, I cut the lead down a little.
The drumline may actually move up.

There is no slotting. Scores and placements do fluctuate.. usually 2 or 3 groups will switch throughout the last 3 shows... especially if the scores that are close.