Engine Only Stays Running if Key Turned

Suddenly today when I stopped at a time red light, the truck started sputtering and backfiring. it then stalled. I was able to start it back up but I ran very rough for another 10 seconds before smoothing out. 10 mins later, same thing happened at a stop sign. But this time, the engine only stays running if ii keep the key held to the start position. So I just rolled to the shoulder. After it cooled down, I could start it again with some rough running, but a few mins later im back to needing to hold the key over to keep the engine half ass'd running. I tried replacing ignition ballast resistor, also have a new dist cap and ignition coil. What gives??

Update: I noticed my alternator belt was fluttering when the engine was running, so I tightened it by raising the alternator as much as I could. I do notice though that the belt still squeaks even though it's tight now. It's also a new belt. Why would it still be squeaking?... should I clean the pullies that it's on? Or is it a more complex problem like a weak alternator or something....

Also, found this hose disconnected sitting by my carb. One end is connected to the cylinder shaped piece that all the vaccuum lines run to, but cannot figure out where the other end belongs.

Anyway, I symptoms I described I my first post ^ makes me think that my timing Is off. The timing chain is quite worn but mechanic set the timing ahead to compensate, but that was over a year ago, so it could have worn even more now. Do you think it needs to be set ahead again? Or am I way off.

Look on the backside base of the carb, there should be a T connection for that hose. That might be your vacuum leak that was causing trouble before.

I found out the center spark plug on the distributor cap wasn't fully connected. It was actually loosely just sitting ontop of where it was supposed to be plugged in. This seems to have solved my starting issue as well as the stalling at red lights issue. Makes sense because one little movement would change the distance between the plug and the cap, resulting in a change of electric current