Check the supply lines feeding the turbo. You may know already, but the o-rings that supply lube to the turbo are prone to failure. This may not be the culprit though. Keep in mind that you're not going to have the same results that you had with the chip. You may want to check the boots connecting the turbo to the intake manifold...after sitting for so long they may have dry rotted or come loose, both of which would cause a loss of boost and less mileage. If you know someone with a code reader it may be good to pull the codes and see if there's anything electronic. I don't think the injectors will go bad, but it's possible. Have you noticed any missing, excess smoke, odd noises, etc? Since you mentioned blow by, definitely do a compression check.
Well i'll start at the beginning, my truck sat not running, from 4/06-8/08 due to a major transmission failure. durring that time I sold my chip, but ever since I got it running the fuel milage has dropped little by little. I had several expected issues due to setting so long, replace all the fuel hoses, rebuilt the fuel bowl, replaced belt, powersteering which has been a constant battle since I bought the truck in June of 2000, and a few other little things. I began to suspect the turbo the other day when i was working on a friends truck and could hear the turbo spool real good, especially for a turbo w/a terribly distorted turbo wheel. Then I realized I hadn't heard mine spool in several months, I figured my compresor wheel must be toasted, pulled it apart and it looks geat. I didn't mind rebuilding the turbo that has 561k on it but I don't believe that is the issue, it does have some play, and a little oil in it, but thats not preventing me from hearing the turbo spool. Anyone have any sugestions ? It does have quite abit of blowby, so I am going to get a hold of compresion gauge, but that wouldn't prevent me from hearing the turbo spool, and most importantly loosing power and fuel economy (14mpg on a long trip w/3.55 rear empty) 
