If you have that much crap floating around in your trans, might be time to install an extra filter. Years ago they used to install a remote oil filter (think motor filter) into the trans line and would spin on a new filter every so many miles.
I'm told it added many miles to the life of a transmission under heavy loads, which is what your doing. I don't know the procedure, but it sounds simple enough. Would be a lot more simple to spin on a new oil filter then dropping the pan a lot of times, especially if you know you have a bunch of junk floating around in there.

They used to add a filter to the cooling system as well.
Gene