I've found conflicting info as to whether sender only sends to gauge or not. But it appears that what I see on the gauge is affecting the computer. To me the issue is that is almost exactly the same whenever the truck starts from cold. about 3 minutes of normal gauge (low to low-normal back to cold (as thermostat opens) then back to normal. (less movement with new sender yesterday but basically the same). Then boom, to max temp for 30 seconds to one minute, then instantly back to normal. Two-three minutes later, same instant rise, and fall thirty seconds later. Then no more.

If it were an actual overheating problem, why would the temp return to normal so fast, or even after shutting off the engine and restarting? (Maybe bubble would do that, but why two times each and every start-up?