Exhaust leak? Or fuel issue?

[69SCSS]

I've been having this issue with my truck for a bit, but thought it was just because the cab had lost of holes in it. I have since put a couple layers of sound deadener and plugs on all the holes (just about) in the cab. Definitely quieter, but the issue remains.

When I drive the truck I get a slight fumes smell and start to get a headache if I drive for too long (30 minutes or more). My headers (Heddman mid-length HED-69010) are noisy. It pretty much sounds like an exhaust leak, but the guy who did my exhaust said the collectors make that sound because they're thin headers. I've never had a set of headers sound like that before, but I took his word for it at the time.

At this point I don't know what to believe. The truck has good power, starts good, etc. Here's the only 2 possibilities I can think of:

1. The collectors ARE leaking. They are the ball in socket type and honestly don't know if they really are sealing. I've had issues with the bolts working loose to the point that I have lock bolts on the ends to make sure they don't work loose anymore!

2. I need to vent my gas tank. I have a Blazer tank, and I ran the fuel line along the passenger side frame rail to a fuel filter just before the cab (so I can get to it easier), then run the line forward to the fuel pump. I used a Blazer Fuel line for the full length. I have not found any leaks. I am using a filler neck from a Suburban, but it's the later (71-72) non vented cap. I was thinking of putting in a vent tube from the passenger side fitting on the top of the tank, up into the bed with a check valve.

Any thoughts? I was already on the verge of going with ramhorns, but if the headers are leaking, I'm going for it. Any thoughts? Anyone in the Portland / Vancouver area wanna take a ride with me and see what you think? I want to enjoy driving my truck, dammit!

Thanks, Al