LS1 thermostat question

ok I know my gauge on my 99 isnt accurate but I have a hypertech power pac that reads the temp as well

My temp is always 160-170ish while driving and occasionally has hit 185-190 in traffic

The other day at Lancaster it went from 170ish to like 220 in about half a second and then dropped back to 160ish just as fast, I watched it do it several times but no other problems

Today I took the car out and the temp only hit 110 after about 5 or 6 miles so I pulled over and popped the hood, the engine felt hot, the radiator hoses were hot but both the hyperpac and the gauge said the same, it stayed between 80 and 110 for the next 4-5 miles until I pulled over, popped the hood and shut the car off, everything felt fine and upon restarting the car both gauges went up to the 170-180 range

The car ran fine and made good power but on the way home it was doing the 170 to 220 back to 170 ect

Any guesses?

Thermostat sticking?

Sending unit going bad?

I ordered a 160 Hypertech unit since it still has the stocker in it

If the new Hypertech T-stat does not solve the problem.I would take a close look at the wires coming from the temperature sending unit.Their should be 3 of them.Could be one of them wires suffered some damage.

If the TSU is stock/original i would consider replacing it with a new AC Delco unit.

Good luck and let us know what you find out.