the 18K unit is a boxed version of a DIY mod that will cost you around 50¢ to do yourself or less than $10 with a switch or potentiometer.
If you're pressed for cash look at picking up a TS chip from ebay, you'll be able to find them for around $200 with a bit of time spent shopping. When you get ready for more mods most tuners (except DP tuner) will be happy to put better and more custom programs on that chip.
The Extreme gizmo from Dfuser seems to be something to alter the injection timing which can give you more power but can also cause severe harm or lack of power if changed too much, not to mention EGT issues.
If you are yearning for mods then i would suggest doing the supporting mods like gauges, Intake & Exhaust, trans cooler, etc... first then look at more fuel.
the 10K or 18k mod (radioshack resistors), zoodad and other mods would be good inexpensive (or free) mods that would bid you a bit more time.
With the econo tunes (DP Tuner or any one else) you should be able to tow safely but you'll need to watch your EGT's & trans temps, And this tune will not be a problem at all for your wife to DD around as in those situations EGT's are not really a concern since you can't stay in the fuel long enough to get really hot.