<<Now, (within the last couple weeks) I have a chatter type noise when the tranny shifts between second and third..... >>

I had a noise coming from mine that sounded like a rumble when it upshifted from 2nd to 3rd. My car's problem was a clogged trans filter and cooler. After they replaced the trans for the second time and installed a new cooler the problem "seems" to be solved. The 92-93 SVXs had trans coolers that were prone to clogging so an inline filter was added. If your's is of these model years you may want to see if you have a filter. If you don't you cooler is likely clogged and there is no way to unclog it satisfactorily. If you have a filter it should be replaced every 30,000 miles. If you don't ever recall it being replaced it is likely clogged.

Not knowing your model year that's about all I can tell you. If you would like a line on where to pick up a stock filter let me know.

Good luck,