Ok so about 2 weeks ago while driving with the ac on my battery voltage light would randomly come on and off. I thought maybe it was an electrical malfunction so like an idiot I continued using it. Ffw a week later, I'm on the highway and loose allllllll power had to be towed home. So here I am now. Battery tested fine so I figured the alternator. Replaced it yesterday and now I have no power no lights no gauges no crank no start. My antithieft light is not even blinking anymore. I'm lost please help

 

Use a multimeter/DVOM to read battery voltage. It should be at least 12.6v.
Keep one multimeter probe on the positive terminal of the battery, then put the negative probe on the alternator. Does it read the same voltage as the battery? It should, if not then you likely have a ground problem.
Can you start the truck with a jump? If you can get the truck started, read the battery voltage with the engine running. Should be at least 13.5v, and 14.7v is not uncommon.
It sounds like you have a bad ground.