Have you verfied your speed with a GPS unit in both vehicles?  I would look a t the speedo and tire size like some have pointed out.  
 

> Date: Mon, 9 Jan 2012 07:59:24 -0700
> From: finnrunyon@GMAIL.COM
> Subject: Oil in Coolant
> To: vanagon@GERRY.VANAGON.COM
> 
> Thanks in advance for your ongoing support of this issue. Those who have
> been following this issue may remember that I moved from NJ to Taos, NM
> last summer. I purchased a second Westfalia upon our arrival out here
> because our 87 has serious rust. The 87 is an automatic, the 89 a 4 speed
> with positraction and Rhein 15" wheels. Several questions, Now that there
> is no further migration of oil into the coolant since I changed the oil
> cooler, I am trying to get a feel for the performance of this engine. At
> 7000 feet here in Taos, I believe that the hp loss is around 21%, vs my 87
> automatic at sea level. I imagine that the 89 also feels a bit slower due
> to the 15" wheels, but I can't directly compare the two as the 87's front
> end is apart. Is there anyone listening that is at a similar altitude. I
> would have no problem getting to say 75 mph at sea level in the 87. If
> feels as though 75 in the 89 is unreachable? Where I am going with this is
> wondering if the overheat that the previous owner did damaged something
> else?
> 
> My second issue is at start up. The bus will start and idle pretty
> smoothly if I let warm up a bit. If I start it and try to move without
> letting it warm up fully it stalls and is cranky to get going again without
> some throttle input. Once it is warm, it runs pretty smoothly. Is there
> something I should be looking into for start up. I don't remember the
> choke situation, but it acts as if the fuel injection is not compensating
> for a cold start?
> 
> Thanks,
> Finn