Presuming you mean SLC-PVR roundtrip (and not the other way around). These are already enormously popular travel days due to many people getting the week between Christmas and New Years off and wanting to spend Christmas day at home. This year, they also fall on a Saturday which is another big travel day as that is when many weekly rentals turn over. Couple that with the fact that DL is still middle-seat blocking coach seats for these flights (they are X'ed out) and this is hardly surprising. Outbound flight 1856 on 12/26 is less of an issue than the return flight as it is currently Y9 B9 M9 H9 Q7. Return flight on 1/2 is main problem and is now completely full in coach/C+ and only has 3 seats left in F (J3 D3 I1). There's an option for around $800 for mid-week travel (K outbound, L return) from 12/23 - 12/29 as these are less popular travel dates.