maybe check the vacuum modulator, or the hose going to it. that could cause symptoms like that, if you have a shop manual it can tell you how to check it,
Im just going by memory here, but i believe it is located behind the trans oil pan on the passenger side. the hose going into it should just pull out, and then it unscrews from the trans.
to check it, i believe that all you have to do is turn it upside down and see if any oil comes out the end that you just took the hose off of, and also check the diaphram with a vacuum guage.
dont quote me on this, cause im just going by memory of what i read(about 4 months ago) in my shop manual for my 92.