Tennessee compares limits, not damages, to decide underinsurance, never stacks across vehicles, and gives you only one year to sue
Tennessee's rules are in T.C.A. 56-7-1201 (required UM, stacking and how UM pays) and 56-7-1202 (what counts as uninsured). The deadline is in 28-3-104 and the extension for minors in 28-1-106.
Read how stacked and single-limit coverage differ in Tennessee, check what section 56-7-1201 says, or see how Tennessee UM and UIM work.