I had the same issue...condenser issue. After researching all of the "design flaws" that were possible, and adding some dye to the system, I found the culprit on the top drivers side of the condenser. The fun part was finding a worthy condenser. I went to a couple of parts houses and opened every condenser they had in-stock for my truck. I went through 8 of them before finding one that was straight! 7 aftermarket condensers came out of the box warped and one AC Delco Professional condenser that had a bent pipe. The second AC Delco Professional condenser I got (had to order it) came out of the box perfect. Now I've been working on cars for 30 years...and I have to say that my truck has the first AC system I've seen without a Dryer can. The Dryer is actually part of the condenser. I don't know how many have noticed, but the AC compressors on these trucks aren't large at all. I replaced the compressor since I already had the system apart. Replaced it with an "Improved Design" AC Delco Professional compressor. So, while the entire system was apart, I flushed out the plumbing and evaporator core and ran compressed air through everything until it was all bone dry. The one thing about this system...it is VERY particular about the measurement of the oil/refrigerant. The new compressor came with 1.4oz (or 1.6oz) of oil, but according to the setup, it requires 2. So I got a measuring glass and got exactly 2oz oil in the compressor, 2oz oil in the condenser and 2oz oil in the evaporator core. I sat the condenser sideways for the oil to get down to the dryer (about 20 minutes), reassembled the system and pulled vacuum. I must say, I really like the design of being able to remove the condenser without having to drop the radiator. I thought the engineers deserved a "hi-five" for that one, hehehe. Anyway, after drawing a vacuum and eliminating the humidity in the system, shut down the vacuum and verified that the system held a -28 to -30psi for a good hour. Installed the right amount of refrigerant and its been blowing ice cold ever since. I got the AC Delco parts from XL Parts.
-TheImpalaMan