I was towing my trailer this weekend and after about 100 miles I noticed what sounded like a hissing noise for a couple seconds.

After the noise I noticed it felt slugish. When accelerating it doesn't do much until about 2500 rpms. After about 2500 rpms I can feel a little boost.

I changed the fuel filter (7800 miles) and it helped but didn't cure it. The air cleaner looks fairly clean but I'm going to change it anyways.

Other than feeling sluggish,the truck is running fine. The MPG is right about where it usually is.

I don't have a boost gauge yet so I really can't say for sure its not making enough boost,but it sure feels that way.

 

You may have a boost leak somewhere. Take it out and go WOT a few times to see if you can duplicate that hiss. If you can, that is probably what it is.