Hi All,
I bought a 1982 GMC C1500 about 2 months ago. I bought it from the original owner, it has 77,000 miles on it and is incredibly clean and original. It was sitting since 2005 when I got it and have had to do some things as well as general preventative maintenance. The old carb had a warped air horn that was causing an internal vacuum leak, and the choke was not working properly (electric choke was getting power). It has a 305 with a Turbo 350 behind it.
Anyways, I think the vacuum modulator on the Turbo 350 might be going bad. Sometimes when accelerating lightly in traffic, it will shift into second, then short shift into third, immediately lock up the converter, and then drop back down into second and accelerate normally.
I've gone through and replaced almost all of the vacuum lines. Part of the maintenance I did was dropped the trans pan, replaced the filter and gasket, cleaned out the pan, and refilled it with new fluid. The old fluid was a bit old and brown, but not too burnt smelling. New fluid has been in there for a few hundred miles and looks and smells good.
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