Hey Mitch ~
I had the same problem, couldn't figure out why it wouldn't budge. The factory puts a layer of glue on the bottom of the tub to sit directly on the plywood and once I put my tub back in without it, it made sense. In order to get my tub out, I had to use a metal yardstick as a wedge and bang on the end with a hammer. Took some time but it eventually came out. Best of luck to you.
4CU 2699 / AIR 10 / TAC AZ-1
I'm haunted by aluminum.
Charter Member of the 4 Corners Unit.