Chris,

You should go ahead and change out the coolant temp. sensor if
unplugging it appears to solve your problem.  It's $12 bucks including
the o-ring and real easy to swap out (be sure to get the o-ring). 
You'll need a short/large bucket to go underneither to catch the coolant
that comes gushing out (anywhere from a pint to well over a gallon). 
You'll want to be sure to do this when the van is VERY cold (let it sit
overnight).  After you've put the new one in, you'll need to bleed your
system of air and replace whatever coolant came rushing out (if you were
lucky--and caught the coolant in a clean bucket--you can reuse what came
rushing out when you pulled the old sensor out).

Your symptoms aren't exactly the same as mine when my sensor was bad,
but yours may be in an earlier stage of deterioration.  Mine worked
great for about an hour, then, when quite warm, would exhibit a severe
loss of power leaving me stranded on the side of the road until it
cooled considerably.  It was a self-preservation feature.  The sensor
was telling the brain that the engine was too hot (it wasn't) so the
brain was shutting down trying to keep the engine from frying.

Good luck!
Tonya
87 Vanagon GL Wolfs
74 S. Beetle