This sounds more like the length of tubes on the headers and/or the diameter was to large. One thing to remember about headers. Longer, and larger diameter tubes are meant for large displacement engines. They also respond better with a higher lift cam, more compression and a 4bbl carb.

Part of the whole tube size equation is factoring in what you use your truck for most. Everyone needs to start from a dead stop, and accelerate. A mid-length header would be the best of both worlds, but is not always available. For most of us, a shorty set of headers with small tube diameter would suit 95% of the driving we do. Most of us do not spend a lot of time at high rpm's, (3000+) which is what a long tube header is designed for.

On a side note, a header by itself is often disappointing. While it is one of the easier modifications to make to an engine, it's not always the most effective.

A decent RV cam and moderate sized 4bbl carb and dual plane intake will wake your truck up a lot more than any set of headers, in terms of power and mileage. Headers would only compliment the previous, where, by themselves, they may leave you a bit disappointed.

 

The headers I used were the cheap Flowtechs from autozone. I should have gotten the 16 guage hedmans, but I didn't.

The reason I did it was cost. When I put the 351w in, I used the old 302 manifolds and tried to split the y-pipe to make it fit. It just did not work right. I checked around, and could have gotten 351w manifolds from the junkyard for 50-60 dollars apiece, and then could have bought the y-pipe for I think 150. I bought the headers for 105, but they turned out to be a big can of worms.

I had to put a big pipe in the end of the header after I mounted it, and bend the driver's side down, since it was hitting the auto tranny oil pan. To hook a pipe to the passenger side header, you have to squish the top of the pipe a little bit with a hammer, because it is so close to the crossmember.

The first go round I made my own y-pipe and hooked it up to the original cat. I ran this for a year, but it looked terrible, since the headers come out so low, you can see all the exhaust hanging down under the truck.

The latest version is I went to duals. I haven't got it inspected this year yet, so it may fail. I went to a local Midas shop and got a quote to do it, and they would not. They would make a y-pipe and then spread it back out into two in the back for $500.00. That is ridiculous.

So I made my own exhaust out of all the little elbows and 45's that you get at the auto store. It ended up costing me about $80 with the 19.95 turbo mufflers, and it surprisingly doesn't look too bad. I ran the exhaust under each of the frame rails up front, and then kicked it up in behind the rocker panels under the doors, and then ran it on the outside of the frame and it exists in front of the rear wheels. At least you don't see much of it hanging down anymore.