Have not seen a lot of post about Flaming Gorge, so here goes
took a guy that has never fished FG before was there 3 days Tue, Wed & Thur
fishing and catching was good,
biggest lake trout was 25 lbs,
we got Kokanee's, rainbows and one Burbot. and one 19" brown trout

most of The kokes we got were only 18 to 19" and just under 3 lbs

I put down riggers down where the water temp is 54 are 52 Deg.

if you can read this you can see where are down riggers were at and were catching kokanees. Orange was best.
Species:
Probe Depth: 46.0 F -----down rigger ball
Probe Speed: 2.2 MPH
Probe Temp: 52.5 °F -----Temp. at down rigger ball
Time: 7:02 AM
Lat: 0.00 Long: 0.00
Notes: surface temperature 64

Species:
Probe Depth: 41.0 F
Probe Speed: 1.5 MPH
Probe Temp: 52.6 °F
Time: 8:38 AM
Lat: Long:
Notes:

Species:
Probe Depth: 49.0 F
Probe Speed: 2.5 MPH
Probe Temp: 52.0 °F
Time: 9:06 AM
Lat: Long:
Notes: surface temperature 64.8

The Temp at 30 feet down was 54 deg.
so down riggers were down 30 to 46 feet most of the time.
I have 4 down riggers all line set backs were less than 35'