new to e99 and diesels in general

[strngcru99]

i just picked up a very clean and unabused 99 (3/98) f350 crew cab 4x4 with 103k there is less then 5k on the new transmission. it has a cold air intake, banks 6 gun and banks trans comand. it still has the stock exhaust which i plan on straight pipeing until i gather the money for a system. what size exhaust should i go with?4" or 5"? im not to worried about loudness per say i just want to keep my egt's down. what else should i look into doing im not looking to make a race truck but want a reliable truck that is also able to tow my bosses 36' 5th wheel with a monster truck and 6quads inside approx 23k. any input would be great. another question should i used the trans comand by-pass plug when i dont have a load on it? it shifts nice and firm now but i think it might be to firm with no load and really dont want to trash the new tranny.

[dieselcrawler]

Stock exhuast is fine, once you straight pipe it, untill you hit the 400 hp mark... the stock muffler is the bottle neck, and a replacement exhaust isn't 'really' needed untill you start making big HP.

Straight pipe it, do the DIY/6637 air filter ($50 or less), add some gauges ($350 or so), and a good tuner ($400-450), (I have a DP Tuner in the yellow truck, and like it, been there about 4 years now) and you will be pleased with the results for about $900 total, if you can do the work yourself.