I haven't built my bumper yet. I dont think the small amount of airflow to the radiator will effect the engine coolant temp because at speeds lower than 5 mph when rock crawling, there is no real airflow besides what the fan is drawing in and the winch will not block/effect that air.
Plus, the truck is built to tow a lot of weight and as long as your not pulling what it's meant to pull, then the small amount of air deflection that may be caused shouldn't effect engine coolant temp either.
The tranny cooler was my concern. However, it does not block enough of the cooler to make a difference if you ask me. Plus, if it does effect the tranny temp by more than 5 degrees then i'll relocate and add a small fan just in case.
I might do a test by checking operating temp of trans pulling a small trailer at 55mph on the freeway vs w/o the winch mounted and see if a tranny scan gun can pick up the temp difference...that would be the true test. If i get a chance to do that this summer, i'll post the results....whether they favor me or not