Other than tires, exhaust etc. I'm his mechanic. he brings it to me for everything. so I don't think anyone else has worked on it.
But I have good news I think. I went back out to look at it tonight.
I took the top cover off the dash by the windshield and looked at the grounds. there is one on each side. The passenger side one was tight.
But the drivers side one (the one people find loose in YouTube videos) was very loose. I barely touched it with a wrench and it started turning! And also, there was a piece of sound deadener under it! Just like I saw in YouTube videos. So I took the nut off, cleaned the deadener off and put the nut back on. I really hope this does it!
If it acts up again I will post it.
Thanks for your advice everyone.

here is a link to video. the ground I was talking about he mentions at 1:34.

The purpose of this diagnostic is to analyze the performance of the thermostat by using the ECT sensor to determine if the engine coolant will increase at the correct rate, and also to meet the calibrated target temperatures under various operating conditions.

The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, and engine run time are also factored in to determine if the ECT does increase normally and reach the calibrated target temperatures.
Conditions for Running the DTC

• DTC P0068, P0071, P0072, P0073, P0074, P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0116, P0117, P0118, P0119, P0121, P0122, P0123, P0223, P0502, P0503, P1101, P1516, P2101, P2135 is not set.
• The start-up ECT is between −40° and 60°C (–40° and 140°F).
• The engine OFF time is greater than 30 m.
• The engine run time is between 75 * and 25 m.
• The vehicle has traveled greater than 1.2 km (.75 mi).
• The fuel ethanol percentage is less than 87%.
• This DTC runs once per ignition cycle when the above conditions are met.

Conditions for Setting the DTC

• The ECM determines that the ECT has not met its calibrated target of 65°C (149°F) when the start-up ambient temperature was between 10 and 52°C (50 and 126°F), for greater than 1 *.OR
  
• The ECM determines that the ECT has not met its calibrated target of 50°C (122°F) when the start-up ambient temperature was between –7 and 10°C (19 and 50°F), for greater than 1 *.

Action Taken When the DTC Sets

• DTC P0128 is a Type B DTC.
• The Engine Coolant Temperature Gauge defaults to cold.
• The A/C is commanded OFF and inoperative.
• The Cooling Fans are commanded ON.

Conditions for Clearing the MIL/DTCDTC P0128 is a Type B DTC.
Diagnostic Aids

• DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation.
• Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.
• A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT.

Reference InformationSchematic ReferenceEngine Controls Schematics
Connector End View ReferenceComponent Connector End Views
Description and OperationCooling System Description and Operation
Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type ReferencePowertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool ReferenceControl Module References for scan tool information
Circuit/System Verification

1. Verify the DTC P0116, P0117, P0118, or P0119 is not set.
   • If a DTC is setRefer to Diagnostic Trouble Code (DTC) List - Vehicle
     
   • If a DTC is not set
2. Verify the cooling system is filled to the correct coolant level. Refer to Cooling System Draining and Filling and Loss of Coolant.
   • If the coolant level is not correctRepair as necessary
     
   • If the coolant level is correct
3. Engine running for 15 min with the A/C OFF, increase the engine speed to 3,000 RPM.
4. Verify the scan tool ECT Sensor parameter is greater than 80°C (176°F) .
   • If less than 80°C (176°F)Replace the Engine Coolant Thermostat.
     
   • If greater than 80°C (176°F)
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
6. Verify the DTC does not set.
   • If the DTC setsRefer to Circuit/System Testing.
     
   • If the DTC does not set

I know the links wont work on the previous response. Still sounds like either you have a bad t-stat or air. Does this engine use coolant or loss of coolant. Had LT engines with coolant from around the outer head bolts. These would also leak from the top corners of the radiator due to pulsing of the t-stat. Also see there is a P06DD. This uses a 2 speed oil pump and have replaced oil pumps for this.
Hope this info is helpful.

It'* been a while, but I changed the thermostat again and cleared the codes about a month ago and everything is good. no more problems at all. the thermostat I put in before must have been bad! Funny how stuff like this can have you chasing your tail. but like they say "always check the obvious first", or something like that. I didn't even think to check if I had a bad part. Cost me a lot of time. I was just confused by all the codes for a thermostat.
Thanks for the help

Wow!

What brand was the bad one?

I don't remember but it was aftermarket bought from RockAuto.

Ah okay. Those could be anything.

At least it didn't get stuck closed.