7.3L ECONOLINE VAN performance help

[in2kelp]

I have a 2001 E350 7.3L Econoline Extended Cargo Van with 74K that I have converted into a "camper van". Basic paneling and insulation throughout, 5 inch suspension lift with 285/75R16 BFG tires for the many miles of dirt roads my wife & I explore. 3.55 gears. Current maximum cargo loads are basically mountain bikes, climbing/camping gear, 12 gallon water tank, house battery and interior improvements: perhaps 600 pounds plus the two of us.

We currently do not tow but *might* tow a jeep in the future.
I have installed a full set of isspro pillar gauges (pyro, boost & trans)
I understand that due to space constraints the vans do not have an intercooler. EGTs max out on long steep grades going 70 mph on I-15 going through the Mojave desert at 1200 with a typical range of 800-1100.

I would like to optimize and improve the performance of the van. I am not looking for a race truck; just sometime with better drive-ability and fuel mileage while maintaining reliability.

What do you recommended? What is the difference between something like the SCT flash tuner and products from PHP? A few shops in my area recommended the SCT but my research seems to point to the many satisfied customers at PHP....Also, as of Jan 1, 2010 a smog check is required for my California van. So whatever I do must not throw modified codes or needs to be easily return to stock every two years.

I am also considering a 4 inch exhaust with a hushpower muffler and FTE resonator. Any experience on how that would effect EGT's? Performance?

There is no cold air intake upgrade for my van that I have found. I have opted for two replacement K&N filters. Can't say that I noticed the difference. One diesel mechanic suggested I modify/cut the 90 degree stock air intake to allow more flow but I am concerned with sucking up snow or water into the system.

Here is a link to some pictures of the van build and how it is used:
Picasa Web Albums - Steve Kazakos

You ideas are welcome!