ENGINE COOLANT TEMPerature SENSOR

I am looking to replace the coolant temperature sender unit in my vehicle. I already spent money on two sensors that did not work from Napa and Amazon. They keep telling me that their sensors are the correct ones. (TX61) However, I think the TS380 is the correct one. According to the OEM listing this is a direct replacement for the one in the 5.4L engine. I say the two previous ones are incorrect due to testing them with the heating and cooling method. They both read around 24K ohms when cold and only drop about 5k in resistance when heated. According to several forums the cold resistance should be around 2k. Can an expert this before I purchase a new sensor? You can also e-mail me at mark. Burns@insitu. Comas well. Thanks.