I realize that this post is over 4 years old, but I figured I would come back and give the update to help people having the same situation as I was. I have since sold the truck but I got it running beautifully before I sold it.

Problem 1 and 2 were linked and problem 3 and 4 were linked.

#1 and #2. It was the computer. The new computer (from a junkyard) solved the driveability problems, starting problems, code problems AND SMOG problems - That truck smogged and drove like a brand new truck - amazingly low numbers. I know many posts here say to get the one with the matching calibration code, but getting one from the same model of truck worked for me. I'm NOT saying that the calibration code matching computer doesn't make a difference, I'm just saying that it runs like a dream and smogs in strict CA. It might have been a matching calibration code (have no clue, came off a different year), but it just plain worked.

#3 and #4. It was the old AND NEW radiator. This problem haunted me for about a year or so. Don't know why the old original radiator had the same issue as the new one (never found out). But, I got a brand new Chinese radiator off Ebay and my problem still existed. I finally found that the filler neck wasn't completely flush where the seal of the cap was - thereby it wasn't pressurizing fully AND it lost vacuum when it was supposed to draw coolant back in. I actually bought a billet filler neck of high quality and had it welded on in its place. It did the trick until 2K miles later I sprang a leak in the radiator not related to the filler neck. Word to the wise - it matters where you get your radiator. DONT BUY CHINESE crap! I ended up spending a bit more and getting a lifetime unit from Autozone. Worked great.

Paul