1991 Chevy S-10 Temp gauge is going crazy.

Engine problem
1991 Chevy S-10 4 cyl Two Wheel Drive Manual ?????? miles

Hi my name is daniel. i have a chevy s-10. The mileage on my truck is really unkown. It does have over 246,000 on it though. But im writing cause im having a problem with my temp gauge. Not to long ago i had to replace the head gasket on my truck. But last night i went out playing in the mud and got my truck stuck. I tryed getting my truck out of the mud but i couldnt. But needless to say i got pulled out and on my way home i looked and i noticed my temp gauge was very high. in the danger zone. so i brought it home and sprayed cold wayer on my ratior. so i thought it was my temputar gauge cause i looked at my dipstick and no visible water was mixed on my oil. Cause it would be milkie lookin and it just looked black. so i went out today and replaced my theromstat. Well that didnt do the trick. not my temp gauge is going crazy and i noticed that my exust manifold is cherry red every time i shut the truck off. I have no idea whats happening and i would really really love to have ur help. I dont know what to do anymore.