I have another vote for the DIY/6637 air filter/intake... simple, easy to install, cheap, HUGE air flow diffrence. It's the first mod I make to my trucks. Straight pipe the exhuast too... air has to get out as much as it can get in... not unreasonable increase in noise, a chrome tip with some 'muffler' design that was on the shelf at the local parts store take the edge off to satisfy me, others will recomend a Walker BTM muffler, it's straight thru design, as large as the stock exhaust pipe, and flows good. The bottle neck is the stock muffler, goes from 3.5" pipe before, down to 2.5" at the muffler, back to 3.5 after it's out... dumb design.
I like the DP Tuner I have on my yellow truck... not too fond of the Edge Evo that came on the Excursion, it makes the trans shift funny, I plan to switch to a DP when the funds are availible. Have nothing on the red truck yet... like the Excursion, it's gonna get a DP when I can afford it.
Gauges are a must before any tunes... with the increased performance, and higher exhaust temps, you gotta know what's going on inside the motor. Summet sells a kit, 3 gauges (boost, EGT, trans temp), and piller pod, for about $330, worth it if you are ok with the increase in bliind spot of the 'A' piller. I have this on my yellow truck, not crazy about the blind spot, but it works, and I'm used to it now. It does put the gauges in an easy to see place.
Good luck, keep us posted on your progress... how about some pictures of the new ride?
'99 E350 DRW Stahl 11' util box van, 7.3 PSD, stock. 138k SOLD
'00 F350 extcab, 9' utility bed, dually 221k
E'99 F250 extcab, S/Bed 211k
'00 Excursion Limited, 7.3PSD 281k
'84 Chevy K-30, 6.2L TD, woods/trail beater. 141k