Stock water temp gauge trouble

[blazer2007]

I have a stock 350 that is fairly new and I put a new rad in this spring and now the gauge slowly pegs to overheating but the headers are hot but can touch them and the coolant is hot but not boiling hot. Both hoses are warm. What do you think, gauge just not good no more, or the sending unit is touching the back side of the head maybe. ( I did have it out to drain water ) This is the first start up since I parked it last year.