Chevrolet Repair: turbo-400 trans., vacuum leak, vacuum hose

Question
I've got an '89 chev. K2500 4x4, 350/400 trans.  The truck sat a year before I bought it. After I ran it around for a while it started not wanting to up-shift from second to third. If I pulled the shifting lever down to second then back to drive, or tromp on the gas pedel like kicking down a choke it would shift up and might be o.k. for a week or two or maybe do it again the next time I stopped. I put some trans-medic in it[ 1/2 a can ] and it straightend out for a while. The longer it sat the more it didn't want to shift. Finally I pulled down the pan, changed the fluid and filter and changed the modulator, but when I was in there some one had the wrong bolt holding the filter and the tube from the right front corner of the filter that went up into the trans.,pick-up tube? kept falling down and will not stay in place. After I put it together it was ok for a couple of days shifting , now it's worse. When it's cold it shifts fine. Once it warms up I think it only shifts by the govenor,about 32 mph it'll shift to second then I can get it to shift to third by moving the shifter about 50 mph. If I let off the throttle it drops back to second. Can I fix it or should I just change the trans.?

Answer
Actually, it sounds to me like you need to follow the line from the vacuum modulator up, and replace some of the rubber hose parts. I would even stick a vacuum guage on it to see what it shows. You may just have a vacuum leak somewhere.
You could try connecting a little mechanical vacuum pump, the kind you test vacuum operated accessories. Just use a long piece of vacuum hose, and keep the vacuum pumped up. This is connected directly to the modulator. If it shifts good then, look for the leak elsewhere.
Good luck,
Van