TT keeps changing rental from 27.5 to 40 years. I always used 27.5. Also TT changes depreciation amt from $2658 to $1700 and puts $958 in Adjustment preferences.

I dont understand the AMT.  I know it changed this year.  Why is is changing my depreciation life of the rental property to 40 years and making an adjustment /preference.  Is the adjustment a tax I pay or is it a carry over.