I'm not sure if this is normal behavior of the sled but when I put my wife's 550f in reverse (especially when cold) it stalls the engine completely. I need to keep the rpm's up in order for it to go into reverse w/o stalling. Do they all act this way?... I don't like keeping the revs up when it's changing into reverse but it seems to be the only way....

yes when the sled isd cold it happens. any other time it is not normal to stall.

When I first start the sled to back it out of the trailer, hit the RER button with half choke. It always works for me.

All the fans are really cold blooded. you got to let them warm up pretty good