If the system was open for a while then trash clogging the expansion valve is most diffinately the problem, also the reciever/dryer bottle is no good because it has lost its ability to absorb moisture(its saturated already).
Was the low side pressure 0 or was it pulling a vacuum? well no matter.
The fix in your case would be to replace the expansion valve and drier bottle. the bottle is located on the drivers side of the condenser, behind the grill. you will have to un-clip the grill, and remove the corner lights to get to it. while the drier bottle is off and the evaporator is removed for the exp. valve replacement, blow compressed air through both lines to try to remove any remaining debris so the new valve wont get stuck. It would be a good idea to remove the lines going to the compressor, so you arn't blowing that crap into it. Replace every o-ring where a line was removed. should be 8 o-rings total, if i counted correctly. You can take the orings to the dealer to get the right ones. they wont rape you, the correct o-rings should be $10 or so.
To get to the expansion valve, you will have to remove the glove box, and the metal support that it attaches to. then a few 10mm nuts/bolts at the bottom, a couple more on the top, and 2 or so going to the heater box. you may have to remove the ecu and a few other things to get the clearance necessary to finagle the box out. Once it is out, there will be 5 or so phillips screws and 4 metal clips holding the 2 halves of the box together. split the box, remove the evaporator and valve together. seperate the 2, and blow compressed air through the evaporator, put it all back together and recharge the system.
hope this helped.
Damn, just noticed your truck is not a taco. Oh well, some things may differ but it will be a very similar.