I have a 2001 HO ,6 speed that I tow a 6,000 lbs. trailer with.
I already have EGT / Boost gauges installed. The only mods. I
plan to do are Edge EZ and BHAF. Do I really need the 4"
exhaust or can I get by with a straight pipe or straight-thru
muffler. Thanks for the help.

 

I would hold off on the 4". Probable be ok...and you have the gauges to tell you where you stand, Can always be done later if towing gets a little hot! Straight pipe is usually done for sound...don't know (have not heard it mentioned) that it will do anything for EGT's?
RJ

 

With just an EZ upgrade you should be o.k. with stock or for a mild decrease approximatly 100 degree drop in EGT's a straight through pipe, but beware if you tow the noise can and does get annoying in my opinion. You could always get a straight through muffler from www.summitracing.com or jegs or many other places.