Newer model I'm asuming you are refering to a superduty rather than the 94-97 style. The 10k trick doesn't work as well on the superduty as it does ion the 94-97, and actually it doesn't help some 94-97 much either. It is a good mod, but makes the foot pedal really senstive. If you are looking for cheep power that is a good place to start. However there are much better alternatives.
Deffantly start with an intake. I reccomend a TYMAR intake form Dale Isley in Spokane WA. You can do a search on thedieselstop, and you will find he is highly reccomended.
There is a wide range of chips and programs to choose from. The hypertech and supertuner work really well! You can pick them up pretty cheep off e-bay as well. My recommendation would be a 3 or 4 position chip. Either TS performance or Bill's custom burn chips. Bill I guess helped with the Ford programing of the PSD, and now is working with or for edge. His burns make lots of power and tend to be cooler on EGT's.
of course, number 1 rule is to get gauges first!! If he has an auto transmission deffantly get a transmission temp gauge. The E40D and the 4R100 really have problems holding to toegather. The best transmission builder for those would be Brian's truck shop in Lead Hill Arkansas. Top notch builder!
Another option is injectors. However I'm really not convinced this is the way to go with towing. The tend to get hot quicker, and the cheepest set of performance injectors will be around $900. almost twice as much as a good 4 pos. chip.
lastly if all he is looking for is help when towing, he might check out propane kits. Unless his truck is under warranty I wouldn't reccomend it. I think they work well for giving you some good power, extra MPG, and tend to run cooler then a chip would. however they are also more $$ then a chip.
Just some ideas for ya, I used to be one of those die hard PSD boys and tried many of the above suggestions. However I saw the light and do love my Cummins!! Good luck and hope this helps!