You don't list the mileage in the EX, You could be experiencing trans slip in some of the gears. Mine went out last year at around 70k, needless to say I was not happy, and like most didn't have the cash to fork out for a new trans, However I looked at the options and determined it to be much better to suck up and replace it before I was sitting on the side of the road somewhere. You might be lucky that the truck is giving you some warning. You can replae the trans with a stocker (doing the labor yourself) for around $2500, you can put in the HD4R100 from the dealer for about $3500, you can order a JW or a BTS for around $4200 (not exactly sure on price, but close for a base unit) or you can check into the BD or ATS. Personnelly I would go with the JW or BTS for the extra money if you can. When mine went out I had a trip planned in two weeks and JW told me it would take at least that to get one unless I payed overnight shipping for a trans......obviously that was not feasable. I ended up going to the dealer based on a conversation with John as he told me his Towmaster is similar to the HD4R100 from the dealer. I put it in and have run it for a year with no problem (which it shouldn't have), You can replace your fluid and do some checks but the end might be inevidable. One other thing to consider is a chip or tuner that also tunes the trans. DP-Tuner and BTS make a chip that you caninstall to give a bit of power these also adjust the shifts and increase line pressure helping the trans grab and go. You can get these for around $300 and up, depending on what you get. If you have never had a chip/tuner you will be amazed at the potential your truck has, one word of caution though is to get a set of gauges to keep and eye on Trans temps, EGT, and Boost. That would be another $400 so not a cheap set-up but definetly worth it when towing.
Changing the trans yourself is not that bad of a deal. Invite some strong backed friends over, rent a good trans jack and work it like a car. You can seperate the transfer case or pull it as a whole unit. Removing the transfer case is much easier I think, but to each there own. To give you an example if you take your truck to JW trans, he removes your trans, rebuilds it, and installs the rebuild unit in a 8 hour day. So if you get everything ready and have what you need a weekend to swap the trans is all you really need. You can save yourself about a $1000 doing this.
Make sure you flush the trans cooler or replace it also. Often times it can have junk in it that will take out the new trans, Look at installing a in-line filter also when doing this to help keep any bad stuff from getting back into the new trans, These filters are anywhere from $30 for a throw away to $200 for a spin on replaceabe kind, Take a look at Dieselsite Transmission Filter System Ford 1999-2003 7.3L
for one option and dieselmann's Store: Filters
Good Luck and hopefully this wil answer some of your questions