Why will the truck not start when the temp gets 20 degrees but it will when I jumped what do I need to do

1. If you can jump start the truck to get it started but not start it with the current battery then you battery is most likely bad and needs to be replaced. (See 2 also).

The problem is the battery is most likely not producing the CCA (cold cranking amps) and CA (cranking amps) that it is supposed to and did when new .( These CCA/CA ratings are listed on the battery label.) In that event you will never be able to start the vehicle.

A basic voltmeter and basic load tester won't tell you if the battery is failing to produce the required CA / CCA to get the vehicle started. Both can indicate your battery is quite passable and OK until a CA/CCA tester is applied and will show the CA/CCA the battery is actually producing which in a failing battery will be well below spec.

2. You should also disconnect the battery cables and clean the battery terminals and cable clamps. If dirty you can get very poor current flow from the existing battery. As a first step check these connections and clean them and eliminate dirty terminals as the cause of your power issue before replacing the battery as suggested.