My first attempt at using lager yeast has hit a wall. I used Zainasheff's dopplebock recipe and two vials of WLP 820 yeast for a huge starter. Fermenting at 50 degrees (with a diacetyl rest at 58 degrees from day 14 to day 18), here is my gravity schedule:

OG = 1.086, Day 16 = 1.052, Day 24 = 1.038, Day 31 = 1.032, Day 38 = 1.028. Transferred off yeast cake, set up fermentation/blow-off in keg. Day 59 = 1.028. My FG goal is 1.020, but I'm afraid I'm stuck.

Any suggestions on how to reach my FG?? Thanks in advance for the help.