Idaho ?

You're welcome. If I can answer any other questions for you, just let me know.

Thanks for the info!

Hey 2stepn, I'm from the Boise area (Meridian) and head up that way often. The best route, is to take Hwy 55 to Horseshoe Bend, continue on to Banks. At Banks, turn East on the Banks Lowman Highway. Take that road till you get to the intersection of Hwy 21, and head NE to Stanley all the way. Avoid Hwy 21 from Boise past Lucky Peak and through Idaho City at all costs. Although it's a scenic route, it's a very narrow road, steep in some places, twisting, with hairpin turns. All the RV'ers in the valley take the Hwy 55, Banks Lowman, Hwy 21 route with ease. Because it's mountainous, there are short sports of climbing with probably the steepest is over Banner Summit, but again, nothing like Hwy 21 through Idaho City. Taking the Mountain Home route to Hailey and Ketchum is doable but not necessary.

The most direct route is state 21 west from Boise directly into Stanley. The western end of that drive is mountainous but most of the way is a nice two lane highway. LOTS of good camping along the Payette River and again, along the Salmon. Of course you said you were heading for Red Fish so probably planning on camping there.

You can miss MOST of the mountainous part of 21 by heading North out of Boise on state 55 then when you are a few miles north of Horse Bend turn east to Lowman. Pick up 21 again at Lowman.
Good luck / Skip

Of the two choices ID75 through Ketchum is straighter, running mostly through a broad valley, with one summit (Gallena Pass)

Idaho DOT lists 4 pass on ID21. I don't find grade information.

https://maps.google.com/maps?q=Redfish+Lake,+Sawtooth+National+Forest,+Custer,+Idaho+83637&hl=en&ll=43.930046,-115.679992&spn=0.016103,0.03459&sll=47.272986,-120.882277&sspn=3.85381,8.85498&geocode=FRs2oQIdalEm-Q&hnear=Redfish+Lake&t=p&z=15&layer=c&cbll=43.930046,-115.679992&panoid=QTLGM0mXpkFKIRL8lVOQTQ&cbp=12,0,,0,0
In this GM Streetview image, the google car is following a low boy trailer around a 20mph curve on the way up to Mores Creek Summit.

Ponderosa Pine Scenic Byway (21)

Sawtooth Scenic Byway (75)

If I remember correctly when the kids lived in Boise they went that direction camping. Some climbs and twists but a good road.