A few days ago I was on the highway for about an hour and started smelling anti-freeze, it passed after a few minutes and I forgot about it. The next day, also on the highway going about 70, I started smelling it much stronger and my windows started fogging up, it wasn't raining and there was no other change in the weather. I pulled over and noticed the cab was filled with smoke, the windows were up. I was 15 minutes from home so I drove it home with the windows open. Once home I checked all the fluids, the coolant was a little low so I topped it off with water, all other fluids are fine (I thought the smell was anti-freeze but wasn't 100% sure, I'm still not). The heat was on while I was driving, I turned the AC on after I noticed the smoke and the smoke persisted. It's a V6 3.0 liter, 80k miles. After I topped off the coolant I started it and looked for leaks and couldn't find any, all the hoses and lines looked fine. It didn't over heat at any point, the temperature stayed normal. I assume the smoke is coming from the vents but I'm not sure, the smoke is thin and I can't even see it unless I get out of the truck and look in. Even when the AC and heat is turned off it still gets smokey. A few years ago I was in an accident and ever since then the heat or AC only comes out of the defogger vents on top of the dash, no matter what I set it to (defog, front vents, bottom vents) it only comes out of the defog vents.

Any help is greatly appreciated, thanks.

Sounds like you may have a heater core problem. Is the floor wet on the passenger side? That is usually a good indication.