Willy the reason I responded that way is because the question is asked 10 times a day, plus you said you searched with little result.
When I used the search feature I came up with:
http://www.explorerforum.com/forums/showthread.php?t=136883&highlight=maf
Says just how much of an improvement was seen with a C&L Maf.
Here's a list of what one guy did to get his 4.0 SOHC seeing very good gas milage and power, gives an idea of what to expect:
http://www.explorerforum.com/forums/showthread.php?t=137531&highlight=MAF
Aldive is ridiculously thorough and has listed everything he did to his truck to get it just over 200hp I believe. Not to mention 30+ mpgs.
There are a number of intakes, there are throttle bodies, headers, exhausts premade and custom, mufflers, gears, tuning, spark plugs and wires, all kinds of stuff you can do that has been covered already on the site.