Clutch oddity

[Richard Segal]

I have a 90 9020V and have been experiencing an 
intermittent problem.  After long drives of approximately > 
160 miles, when I enter back into the city and have to deal 
with red lights and stop signs the following occurs:  when 
sitting at the stop light, I hear what seems to be kind of a 
vacuum noise and when I release the clutch to move 
forward, the car jerks . . . similar to what it felt like
when learning how to use a clutch for the first time.  This 
only occurs after long distance travels.  When I use the car 
as my daily driver in the city only, clutch feels fine and no 
vacuum sounding noise.  Any ideas what is occurring?  
Thanks for any assistance you may be able to provide.

Rich