Yup, frost and a dirty carb or TB.  I have seen that happen from frost
grabbing onto dirt at the linkage or pivot points in carbs and Throttle
bodies.

TB's and carbs can frost up just at that 'vapor point' temperature.

Usually the cable end is gunked up too.  A good clean with WD40 or even
a throttle body spray cleaner should really help it out.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's - Gone to the rust pile...
Canadian Off Road Trips Photos:  Non members can still view!
Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590
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A classis case of throttle body icing caused by the cooling effect of
the expanding air / fuel mixture below the throttle plate(s) is what
you are experiencing.  

This is a common aircraft engine issue.. It traditionally happens more
often when temps are just slightly above freezing and the humidity is
fairly high.

Check all your sources of throttle body heating.. some cars use
the engine cooling water piped into a jacket surrounding the throttle
body, some use exhaust gasses in a similar manner and some have a
"stove" on one of the exhaust manifolds and use a thermostatic
control to pipe hot air into the intake to prevent this problem.

The clue here is that you feel the throttle pedal sticking. This is
being caused by the icing around the throttle plate(s) jamming them in
the body bores.  The restricted flow is what causes the stalling.  The
idle speed control systems on computer controlled engines are also
prone to this problem. After the stall occurs, the engine heat rises
up into this area and melts the ice, "curing" the issue for the
moment!

This problem was extremely common in carburated engines and
was usually worsened by a build up of carbon in the exhaust "riser"
passages that provided hot exhaust gasses to passages under the carb
used for heating the throttle area. These cars usually had a manifold
heat valve on the exhaust manifolds to direct the hot gasses around
the carb base during warm up.

Someone with GM experience with your 3800 will probably pipe in here
with some specific things for you to check on your engine.

I owned a 1955 Buick V8 that was absolutely undriveable in a freezing
rain or snow storm because of this problem.  Removing the heads and
manifolds to clean out the "coked up" riser passages to the heated
area under the carb really helped, but it still would ice if
conditions were right.. Too bad, this was in the days before heated
air intake systems and other corrections for this problem were used.

Let us know what you find...

Bob
Rflumere@comcast.net