according to bass and walleye boats formula with 10% slip and turning a 24 prop 6300 rpm you should be at least in the high 60's.at that speed 60mph the nose coned gearcase is probably hurting you,with low water pick up you need the motor as high as possible to reduce drag,my buddy gad a hydra sport vl475 with a 200 on it and a coned case it ran 69mph,put on a stock case and it gps 73.5.are you sure your tach is right?even if you are running 185 hp it would be hard to get 6200 rpm without a lot of extra slip on that ranger.when you trim it up watch the rooster tail,if the bow don't lift and the tail goes up,start dropping the motor a little and see if it bites better.I would start with the prop shaft about 3 1\2" below the pad and start up from there.you need a gps to really see if what you are doing is working.
test the boat as you normally run it.1\2 tank gas some water in the wells and don't overload the front.
Sorry the post is so long my computer has been down and i havn't been able to post for a few days.