Volvo Repair: transmission, clutch pack, transmission shifts

Question
Hi,
 I have a 1993 with 114000 miles.  It is a great car.  But I have been noticing since it has gotten cold that when the auto transmission shifts from 3rd to 4th there is a slippage.  It goes into 4th and stays there but it slips going in.  Can you tell me what this means and if the transmission is going to give out soon.  Is there something I can put in the transmission to stop this, eg. one of those fluids I see at Wallmart?

Answer
 Don, first it would be nice to know what model you are talking about.

 In general, no additive is going to repair wear. That is what i suspect you have going on in your clutch pack. Low pressure can cause the same effect. If it continues, it will fry the clutch pack. It is worthwhile to try a fluid and filter change and flush before replacing/overhauling the transmission though. Sometimes there is particles (dirt) that get lodged in the valve body orfices that prevent full fluid pressure for proper engagement.
  A "GOOD" (hard to find) tranny guy can hook into the trans. with manual guages and observe pressures while driving. Unfortunately, it seems to be a lost art nowadays. Everyone just replaces them. Sigh...

Mark