Hi Jay I had the very same problem with a Nightforce scope. Tried strap wrench and all sorts. In the end I protected the lense as best I could with discs cut from an ice cream container and sponges. Turned the combi boiler to max, turned on the hot tap, restricted the flow till it was to hot to hold my hand under. Put the offending threads under for 2-3 minutes and sunshade came off a treat.
I cleaned the threads put a little silicone grease on them and after a little work it now goes on and off as it should