Villian was unknown but has been tight for 3 orbits

I think his bet sizing somewhat serves as a tell.

Poker Stars $0.50/$1 No Limit Hold'em - 6 players
The Official 2+2 Hand Converter Powered By DeucesCracked.com

MP: $254.35
CO: $104.90
Hero (BTN): $100.00
SB: $251.50
BB: $59.00
UTG: $100.00

Pre Flop: ($1.50) Hero is BTN with K J
2 folds, CO raises to $3.50, Hero calls $3.50, 2 folds

Flop: ($8.50) 5 K T (2 players)
CO bets $5, Hero calls $5

Turn: ($18.50) J (2 players)
CO bets $15, Hero calls $15

River: ($48.50) 3 (2 players)
CO bets $45, Hero ??