The differences you're seeing are less than 1% in frequency. I think you should try generating a few more Pronto Hex in IrScrutinizer. For example try function 52, which you already know to be Fast Forward. Does the generated signal work? If it does, it tend to cast doubt on 55 being correct. If it doesn't, then the DVR is more finicky than most, and we'll have to try adjusting the timing.
This
Widget-based capture says CM is using NEC1-rnc, Device 1.
1 Power
32 1
33 2
50 3
35 4
36 5
37 6
38 7
39 8
40 9
41 0
30 period (.)
7 DVR
9 Menu
16 Guide
48 Home
14 Exit
15 Info
8 cc
49 Back
22 OK
18 Up
20 Left
19 Down
21 Right
10 Red
11 Green
12 Yellow
13 Blue
5 Page Up
6 Page Down
3 Channel Up
4 Channel Down
26 Rewind
29 Pause
25 Play
52 FF
23 Skip Back
24 Skip Forward
28 Record
27 Stop
2 Audio
31 Window? (Key below 9)