Welcome to the Forum from NH.
Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.
I hope that you will become a participating member in the Forum's discussions.
Pics of the truck, please.
You are already receiving sage advice from the knowledgeable folks on this Forum.
A quick starter test is to have somebody attempt to start the truck, and when you hear the click, smack the starter with a hammer to give it a slight mechanical shock. If it fires up, then it is most likely the starter or its attached (not-replaceable) relay.
"I tested the battery and it's fine." - The only true way to test a battery is to pull it out of the truck, take it to an auto parts/battery store with a bench load tester, and get it load tested. Have you done that? If not, do it, before firing the parts cannon with its associated extra costs.
If the battery load tests as good, then thoroughly check the battery cables to the main fuse, to ground, and to the starter. These cables typically rot from the inside out, so a continuity test should be performed on each cable to ensure that their resistance is very low.
If the main cables check out OK, then check all grounds in the engine bay, including the motor to firewall ground, to ensure that they are clean and tight.
If engine bay grounds are good, then check the ground on the truck's frame, approximately below the driver's feet.