Mark -
You had all 4 wheels spinning on a 7 foot rear blade? What about the BB? I am quite surprised by this. I have read your posts and have seen the work you do with your tractor. I believe that we have the same set up.
I have only been bogged down twice - three times with this tractor. 1) 5 ton stump - way too big for this tractor, and almost too big for this tractor and a skid steer.
2) When I had my home picked up and moved back further on the property we could not salvage the old porch (cement). The slab was about 17' long, about 8' wide, and had a three foot monolithic pour for the footer. Once again, way too big a job for this tractor. Had to get a big case backhoe to move it and snap it in half. Half of it was too much for this tractor. I had a guy take his skidsteer and flip it, which broke it.
3) Logging a maple tree
My BB has never caused my tractor to bog down.
The times you bogged down with the rear blade, were you pulling or pushing? I know you had it in 4 wheel, but did you have the differential lock on? Once I engage that thing my spinning normally stops. Also, are your rear tires loaded?
Sorry for all the questions, but I just got power back on at my house this week (after 9 weeks) and can do more research on my tractor. I had some real issues with it in the last two months. Performance issues I never expected, like lack of traction in mud and clay - like being on ice.