Step 1, arm yourself with at least a 12 pack of your favorite adult beverage. I prefer Yuengling lager or something similar. Natural ice works too. I did half of mine one day. The reinstall the next. Total time working was just about 3 hours or so. This is my first write up so go easy and dont flame me too bad guys.
Remove battery. Remove the glove box. Remove under dash trim/hush panels. Remove speaker covers and screws underneath, defrost vent difuser and screws under it that hold the dash to firewall. Its a good idea to leave one or two in till you're ready to remove the entire assembly.
Remove the bolts holding up the steering column. Some like to remove it all-together. I just loosen everything up and drop it down onto the seat.
Jack front right of truck up and remove right front wheel. Remove inner fender. To remove the inner fender you'll have to loosen the PCM nad part of the battery tray and a few other misc bolts. I didnt remove my inner fender all the way, just enough to be able to reach through and work at the firewall.
Drink beer, admire your work thus far.
You'll need to remove a couple of 10 mm bolts at each end of the dash assembly in the lower corners. Here is where it can get tricky. When I do this I do not remove the radio, inst cluser, hvac controls...nothing. I get under the dash and disconnect everything that I can which is everything but the radio as best I remember. You'll need to disconnect the main elec block on the drivers side (7mm) in the center of the connector there is a bolt. Loosen it, pull it out. I remove the BCM too. While I'm there I also disconnect the vac lines to the HVAC stuff, air bag connectors(yellow) etc etc.
Once you're sure that things are disconnected step back and have another beer or three.
Remove the aforementioned screws at the top of the dash and the entire dash should rotate down/back. The entire assembly sits on two locating pins at the base of each A pillar and the frame for the dash is slotted to fit in there. You'll know it when you see it. I rotate the dash down and lay it on the seat/steering column and reach behind it to disconnect any other wires such as the radio wires and antanae wire as needed. Once you're satisfied everything has been disconnected grab a buddy, gf or wife and kift and remove the dash. You'll be left with firewall, a bunch of wires, a few hoses, a big black box looking thing and a steering column laying on your seat. This is normal.
Drink beer, admire work.
The black box thing is where your heater core is. On the bottom there are a couple of nuts/bolts(10mm) you can remove from inside the cab. Remove/disconnect the vaccum hoses as needed.
Under the hood.
There is one bolt/nut(10mm) on top that is easy to get to beside the hoses.
Go through the hole/gap in the inner fender you made earlier and remove one more 10mm. Here comes the fun part. On top of your box where the ac lines go into it there is an electrical connector. This goes to the resistor for your blower motor. It should have 2 or 3 very small screws holding the whole thing down. Remove those and you will be able to remove the entire resistor and cover. e careful not to damage it. You will be left with a small rectangular hole that is big enough for my 3 year old to get his hand into but not me. Some dealerships/shops will remove the entire assembly that you see to get to this one freakin bolt/nut adding hours of labor. Not me, I'm all about shortcuts. Work smart not hard right? Peer into this opening (you may need a mirror) and you will see several inches down another 10mm. Thats the one you need to get out. I used a 1/4" MAC air ratchet and a 10mm wobble head socket. I had it out in 30 seconds. Dont worry about dropping it in there either since I know I'm taking the whole box out anyways.
TIP: When putting it back in if you choose too, put a piece of notebook paper about the size of a dime on top of the socket opening and force the nut/bolt into the socket. This will hold the darned thing in the socket so it wont fall out whilst you try to put it back in...if you choose to. Some people leave it out.
Once all your bolts/nuts are removed you can remove the HVAC module assembly. Its pretty self explainatory from here. Pop the top open and swap heater cores. Drink more beer, you've earned it.
Put it all back together.
I'm sure I've left some out but thats the best I can remember off the top of my head at 10 minutes past midnite. Anyone else sees anything I've omitted chime in but this should be enough to get you through it if you're halfway inclined.
Here are some pics I took of mine during the process.
The steering column
Two of the bolts/nut you can access from the cab. (box is upside down)
Another location of bolt/nut
Opening in fenderwell
Resistor removed for access to bastard bolt.
Time to drink beer, its out.
Elec connections to remove/seperate (7mm bolt)
Wires and stuff everywhere! Better have another beer.